WO2000042199A1 - Biologically active reverse transcriptases - Google Patents
Biologically active reverse transcriptases Download PDFInfo
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- WO2000042199A1 WO2000042199A1 PCT/US2000/000896 US0000896W WO0042199A1 WO 2000042199 A1 WO2000042199 A1 WO 2000042199A1 US 0000896 W US0000896 W US 0000896W WO 0042199 A1 WO0042199 A1 WO 0042199A1
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- C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
- C12N9/10—Transferases (2.)
- C12N9/12—Transferases (2.) transferring phosphorus containing groups, e.g. kinases (2.7)
- C12N9/1241—Nucleotidyltransferases (2.7.7)
- C12N9/1276—RNA-directed DNA polymerase (2.7.7.49), i.e. reverse transcriptase or telomerase
Definitions
- the invention relates to the field of molecular biology.
- the invention relates to reverse transcriptases.
- RT reverse transcriptase
- Reverse transcriptases are found in a variety of retroviruses. or RNA tumor viruses. Techniques for producing RT from these native sources involve isolation of virus particles which contain about thirty RT molecules per virion. The RT is released from the virions by lysis of the virion coat. Released native RTs may then be purified using conventional techniques. However, the procedure involved in the production of these viruses is labor- intensive and costly (1 ,000 infected chicks produce 10-20 grams of virus, which is approximately 25,000-40,000 units/gram of virus). Additional problems with RT production from natural sources are the high natural mutation rates which, in part, result in restricted host ranges such as specific strains of chickens.
- RTs An alternative source of RTs is recombinant production, which in turn is dependent on an understanding of RT expression by the various retroviruses.
- retroviruses bind to receptors on susceptible cells and insert the retroviral core particle into the cytoplasm of the host.
- Two major events occur in the life cycle of retroviruses.
- the single-stranded RNA genome is converted to double-stranded DNA by reverse transcriptase.
- this DNA copy is inserted into the genome of the host cell (Varmus, et al. , In Mobile DNA (ed. Berg, et al. ,) pp 53-108, (1989), Washington D.C : AM. Soc. Microbiol. 972 pp; Brown, Curr. Top.
- AMV Avian Myeloblastosis Virus
- MAV Myeloblastosis-Associated Virus
- Integrase ensures a stable association of viral and host DNAs. Integration is site- specific with respect to the viral DNA but is essentially random with respect to the host. This observation indicates that there is a DNA binding region in the integrase domain that is necessary for the binding of viral and host DNAs, in a manner independent of host sequence, during the integration process.
- the integrase domain is not found within mature MMLV-RT (i.e. , Moloney- Murine Leukemia Virus Reverse Transcriptase, a Type I RT) or mature HIV-RT (i.e. , Human Immunodeficiency Virus Reverse Transcriptase, a Type II RT). However, the integrase domain is found as an integral part of the mature avian RT (a Type III RT). The presence of this integral integrase domain, along with thermostability. are two features of avian RTs that distinguish this class of RT from other RTs. Investigations of the integrase domain of avian RTs have revealed that it functions in DNA binding and in polymerization, or multimerization.
- HHCC Histidine, Cysteine
- the central region of these integrases contains a catalytic domain which shares homology with bacterial transposases involved in the breaking and joining of nucleic acid molecules (approximately, amino acids 630-807 of SEQ ID NO: 2).
- This region has acidic amino acid residues which have been proposed to be involved in the binding of required metals (Mg ⁇ ⁇ or Mn + + ). Khan et al. , Nucl. Acids Res. 19:851-860 (1991), reported DNA binding activity in this central region.
- the C- terminal region of these integrases is not conserved at the sequence level and its function is unknown (approximately, amino acids 808-858 of SEQ ID NO:2).
- deletion analyses indicate that this region contains strong sequence-independent DNA binding activity as well.
- the integrase polypeptide functions as a multimer, or polymer.
- the N-terminal zinc finger-like domain and the C-terminal deletion derivative have less tendency to dimerize. Hickman et al. , J. Biol. Chem. 269:29,279-29,287 (1994). Sedimentation analyses suggest that integrase occurs as a mixture of monomers, dimers and tetramers.
- the genome of the retroviruses codes for several genes, namely gag, pol, env, and the cellular oncogenes, tat, ars/trs, nef, rev etc.
- the pol gene codes for a polypeptide with reverse transcriptase (RT) activity.
- the RT enzyme has several activities, such as RNA- dependent DNA polymerase, DNA-dependent DNA polymerase, ribonuclease (RNase H), integrase, endonuclease and, possibly, protease activities.
- reverse transcriptase is mainly used for its RNA-dependent DNA polymerase activity, which elongates an oligonucleotide primer, such as a tRNA, annealed to a template RNA or DNA strand to synthesize a DNA strand that is complementary to the template strand (cDNA) (Copeland, et al. , J. of Virology 36: 1 15-119 (1980); Berger, et. al.. Biochemistry 22: 2365-2372) (1983)).
- cDNA template strand
- MMLV Moloney-Murine Leukemia Virus
- HIV-RT heterodimer consists of a 66 kDa ⁇ polypeptide and a 51 kDa a polypeptide.
- the avian RT heterodimer consists of a larger 95 kDa ⁇ polypeptide and a 63 kDa polypeptide.
- the polypeptides from HIV-RT and the avian RTs differ in that the HIV-RT polypeptide lacks RNase H activity.
- the ⁇ polypeptide of HIV-RT and the ⁇ polypeptide of avian RTs differ in that the HIV-RT ⁇ polypeptide lacks the integrase activity of avian RT ⁇ polypeptides.
- AMV-RT occurs in nature in multiple molecular forms, such as monomers, homodimers and heterodimers.
- the major active native form is a heterodimer of two structurally related polypeptide chains, an subunit of 63 kDa and a ⁇ subunit of 95 kDa.
- These mature subunits are the products of post-translational processing of a precursor protein of 180 kDa (Gag + Pol).
- the 180 kDa protein is cleaved to a 95 kDa ⁇ subunit.
- the ⁇ subunit may be further cleaved to a 63 kDa subunit and a 32 kDa endonuclease subunit.
- the and ⁇ subunits have identical N-termini. (Roth, et al. ,J. Biol. Chem. 260:9326-9335 (1985); Gerard, et «/. ,DNA 5: 271-279 (1986)). Beyond a difference in form (monomer v. heterodimer), the avian RTs differ from
- MMLV-RT in other ways.
- the avian reverse transcriptases exhibit high processivity and yield, as well as biological activity (e.g. , polynucleotide polymerase activity) over a wider range of temperatures extending up to at least 70° C. This ability to polymerize at higher temperatures is useful when working with RNA templates that have secondary structures. Additionally, this temperature stability has been exploited in amplification technologies such as NASBA and RAMP.
- Non-avian RTs including those RTs having RNase H activity, have relatively low processivity and yield. For example, it has been estimated that approximately 50 times more MMLV RT is required than AMV-RT for cDNA synthesis.
- the avian retroviruses include Avian
- ASV Sarcoma Leukosis Virus
- RSV Rous Sarcoma Virus
- ASV Avian Sarcoma virus
- ATV Avian Tumor Virus
- helper viruses such as MAV, Avian Sarcoma helper virus UR2AVRT, Rous-Associated Virus (RAV), and others.
- the homology among the avian reverse transcriptases at the DNA level is between 90-98 % and, at the amino acid level, the homology is 95-100% .
- AMV Reverse Transcriptase (i.e. , AMV-RT) has been characterized and conditions for the synthesis of full-length cDNA products have been investigated. Berger et al. , Biochemistry 22:2365-2372 (1983). However, the length and yield of cDNA produced by AMV-RT have reportedly been limited by either a nuclease integral to AMV-RT or associated contaminants. See, U.S. Patent No. 5,017,492. In efforts to maximize cDNA length and yield, attention has turned to MMLV-RT. MMLV-RT is a reverse transcriptase that is relatively thermosensitive and exhibits relatively low reverse transcriptase activity.
- the avian RTs are structurally distinct from MMLV-RT.
- avian RT e.g. , AMV-RT
- the native AMV-RT is a heterodimer composed of a 63 kDa alpha peptide and a 95 kDa beta peptide while MMLV-RT is an 80 kDa monomer.
- these enzymes differ in their thermostability.
- the thermophilic AMV-RT is active over a broad temperature range extending, at least, to 70°C.
- MMLV- RT is a mesophilic enzyme
- AMV-RT and MMLV-RT differ in other properties such as processivity, metal co-factor requirements, error rate (i e , rate of incorrect nucleotide incorporation), and tRNA primer preferences
- the present invention relates to the discovery that reverse transcriptase polypeptides which have been modified, e g , brete ⁇ ng existing integrase domains or by adding integrase domains that is modified themselves, are characterized by one or more improved properties, which include increased activity, stability, and solubility, as well as increased ease and versatility in producing such polypeptides
- the reverse transcriptase polypeptides of the invention may be derived from any source, including, but not limited to, Moloney-Mu ⁇ ne Leukemia Virus (a Type I reverse transcriptase or RT), HIV (Type II RTs), and avian retroviruses (Type III RTs)
- RT polypeptides that are truncated internally and/or at their C-termini, yet retain RNA-dependent DNA polymerase activity, the defining characte ⁇ stic of reverse transcriptases
- the truncated polypeptides may also have and preferably do have, DNA-dependent DNA polyme
- RTs for use in a wide variety of DNA synthesis, amplification and sequencing technologies
- the invention also provides a chimeric RT polypeptide resulting from the effective addition of a protein domain to the C-terminus of the truncated RT, resulting in a non-native chimeric polypeptide (/ e , a polypeptide not found in nature)
- These protein domains provide a DNA binding capability, a metal binding capability, a structure stabilizing capacity, or a polymerization (/ e , multime ⁇ zation) capability and preferably several capabilities With these added or enhanced, capabilities, the chimeric polypeptides of the invention exhibit improvements in RNA-dependent DNA polymerase activity, protein expression levels, protein stability, and/or protein solubility, with chimeric polypeptides of the invention frequently showing improvement in all four properties
- Preferred protein domains include a plurality of histidine residues (/ e , His tags), and either the N-terminal domain (providing a DNA binding capacity, preferably resulting from a zinc finger domain) or the C-terminal domain (providing
- One aspect of the invention is an isolated polynucleotide encoding a polypeptide according to the invention.
- the invention comprehends polynucleotides encoding polypeptides having RT activities, those polynucleotides typically lacking approximately 200-1 , 122 bp of the 3 ' ends of the corresponding native RT genes.
- a full-length avian RT gene i.e.. MAV pot
- MAV pot 2,692 bp (SEQ ID NO: 1) and the invention contemplates MAV-derived polynucleotides of approximately 1 ,570-2,492 bp in length.
- polynucleotides of the invention may result from truncations to RT-encoding polynucleotides derived from any source, including: AMV, MAV, RSV, ASLV, ATV, MMLV and HIV.
- the invention contemplates an isolated polynucleotide encoding a polypeptide having RNA-dependent DNA polymerase activity, the polypeptide consisting of any one of the following sequences: an amino acid sequence beginning at amino acid 1 and terminating at any one of amino acids 428 to 857 of SEQ ID NO:2; an amino acid sequence beginning at amino acid 1 and terminating at any one of amino acids 428 to 1 ,054 of SEQ ID NO: 39; an amino acid sequence beginning at amino acid 1 and terminating at any one of amino acids 548 to 1 , 198 of SEQ ID NO:41 ; an amino acid sequence beginning at amino acid 1 and terminating at any one of amino acids 428 to 901 of SEQ ID NO:43; and variants, analogs and fragments of any of the above-described polypeptides having RNA-dependent DNA polymerase activity, the aforementioned polypeptides (i.e.
- polypeptides and variants, analogs, and fragments thereof optionally having an N-terminal methionine.
- An exemplary polynucleotide has a sequence set forth in any one of SEQ ID NOs 1 , 7, 9, 38, 40, and 42.
- the polynucleotides preferably comprise a start codon specifying methionine at the 5' end.
- Other truncated polynucleotides of the invention have internal deletions, preferably removing at least part of an integrase domain.
- polynucleotides according to the invention comprise the sequence set forth in SEQ ID NO:40, with part or all of nucleotides 2464-3012 deleted, or comprise the sequence set forth in SEQ ID NO:42, with part or all of nucleotides 1840-2708 deleted, or comprise the sequence set forth in SEQ ID NO: l , with part or all of nucleotides 1719-2571 deleted (e.g. , deletion of nucleotides 1860-2310, 1920-2310, or 1980-2310 of SEQ ID NO: l).
- Such polynucleotides encode polypeptides that lack an effective integrase activity in that the polypeptides do not promote detectable polynucleotide integration.
- polynucleotides according to the invention encode chimeric polypeptides, such polynucleotides comprising a polynucleotide encoding a polypeptide having RNA- dependent DNA polymerase activity and an adjacent polynucleotide encoding a terminal modification of that polypeptide, thereby encoding a chimeric polypeptide.
- Preferred polynucleotides encode a chimeric polypeptide having one or more amino acids attached to the C-terminus of a polypeptide having RNA-dependent DNA polymerase activity.
- Such polynucleotides may contain one of the above-described coding regions fused (in frame) at its 3' end to a region encoding one or more amino acids.
- the 3' end of a coding region may be fused to one or more codons for a charged amino acid such as histidine, lysine, arginine, aspartate, or glutamate.
- the 3' end of the coding region may be fused to a region encoding a polypeptide, preferably having four to fifty (e.g. , six) amino acids and preferably comprising a domain selected from the group consisting of a DNA binding domain, an RNA binding domain, a metal binding domain, a polymerization domain, and a structure stabilizing domain.
- domains include, but are not limited to, disulfide bond forming cysteine residues, a zinc finger domain, an acidic amino acid domain, and a basic amino acid domain, a bulk) amino acid domain (e.g. , W or W-H, single-letter amino acid identifications), a PPG domain, a GPRP or a PRPG (i.e. , inverse GPRP) domain, a leucine zipper motif or domain, and an NSl binding site, among others.
- suitable domains include, but are not limited to, the N-terminal domain of the MAV-RT integrase region which provides a DNA binding domain and the C-terminal domain of the integrase region which provides a polymerization domain.
- polynucleotides encoding chimeric polypeptides having a plurality of C-terminal amino acids may encode the same amino acid a number of times. Such polynucleotides may encode basic (e.g. , Histidine) amino acids at the C-terminus. Also preferred are polynucleotides that have a stop codon (e.g. , TAA, TAG, or TGA) at the 3 ' end of a coding region of a chimera according to the invention.
- An exemplary polynucleotide encoding a chimeric polypeptide has a sequence selected from the group consisting of a sequence set forth in any one of SEQ ID NOs 11-19.
- polynucleotides of the invention encode a chimeric polypeptide having one or more amino acids attached to the N-terminus of a polypeptide having RNA- dependent DNA polymerase activity.
- the invention contemplates polynucleotides that encode more than one modification, such as an N-terminal peptide addition and a C-terminal peptide addition or a C-terminal peptide addition coupled to an internal deletion of at least part of an integrase domain.
- the invention also provides a vector comprising any of the aforementioned polynucleotides.
- a preferred vector comprises a polynucleotide operably linked to a promoter.
- Another aspect of the invention is directed to a host cell transformed with a polynucleotide of the invention, such as prokaryotic (e.g., Escherichia coli) or eukaryotic cells (e.g. , insect cells).
- the invention comprehends a method of transforming host cells comprising the following steps: introducing a vector according to the invention into a host cell; incubating the host cells; and identifying host cells containing the vector, thereby identifying a transformed host cell.
- Still another aspect of the invention is a method of producing an isolated reverse transcriptase polypeptide comprising the step of transforming a host cell with a vector as described above, incubating the host cell under conditions suitable for expression of a polypeptide, and recovering the polypeptide, thereby producing an isolated reverse transcriptase polypeptide according to the invention.
- the invention provides the polypeptides encoded by the polynucleotides described above.
- These polypeptides include polypeptide fragments (e.g. , ⁇ RT fragments containing part, but not all, of the C-terminal integrase domain) and chimeric polypeptides, as described above, as well as variants and analogs thereof.
- the invention contemplates all types of reverse transcriptase fragments and chimeras (and variants and analogs thereof) including, but not limited to, the three classes of RTs exemplified by MMLV-RT, HIV-l-RT, and avian RTs.
- Exemplary chimeric polypeptides contain an N-terminal methionine or a C-terminal peptide providing useful functions (e.g. , expression enhancement, nucleic acid binding domains, metal binding domain, structure stabilizing domains, or polymer- forming domains).
- Other chimeric polypeptides according to the invention may result from modification of RTs derived from, e.g. , the following sources of Types I-III: ASLV, ATV, MMLV, HIV-1 , and HIV-2.
- a preferred addition to an RT is a C-terminal peptide comprising a plurality of amino acids such as basic amino acids, a nucleic acid binding domain, a metal binding domain, or a polymerization domain.
- the C-terminal peptide provides more than one functionally significant domain.
- one or more C-terminal cysteine residues which, at a minimum, provide a capacity to induce polypeptide homo-, or hetero- , polymerization, such as dimerization.
- Typical polypeptides of the invention are relatively soluble and are capable of being expressed at high levels, resulting in relatively high levels of RT activity expected to facilitate economical purification.
- Yet another aspect of the invention is an improvement in a method for copying a target nucleic acid by extending a target nucleic acid-bound primer, the improvement comprising: contacting the target nucleic acid and primer with a polypeptide according to the present invention.
- the method preferably produces one or more copies of the target nucleic acid and the polypeptide may be a polymer.
- Any method for copying a target nucleic acid using a polymerase is comprehended by the invention, including, but not limited to, cDNA synthesis, Polymerase Chain Reaction, Polymerase Chain Reaction- Reverse Transcription, Inverse Polymerase Chain Reaction, Multiplex Polymerase Chain Reaction, Strand Displacement Amplification, Multiplex Strand Displacement Amplification, Nucleic Acid Sequence-Based Amplification, Sequence-Specific Strand Replication and Rapid Amplification.
- Another aspect of the invention is directed to improved methods for sequencing a target nucleic acid by extending a target nucleic acid-bound primer, the improvement comprising: contacting the target nucleic acid and primer with a polypeptide according to the present invention.
- kits for copying a target nucleic acid comprising one or more nucleotides and a polypeptide according to the invention.
- Preferred polypeptides include those polypeptides encoded by a polynucleotide having a sequence selected from the group consisting of SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO:38, SEQ ID NO:40, SEQ ID NO:42 and polynucleotide derivatives thereof encoding C-terminal amino acids or polypeptides at their 3' ends.
- Fig. 1 photographically depicts Western blot analysis of RT expression products of insect cells.
- Fig. 2 illustrates recombinant RT fractionated on an 8% SDS-PAGE gel and stained with Coomassie Blue.
- Fig. 3 presents an autoradiograph of gel-fractionated cDNAs produced by an RT polypeptide according to the invention.
- Fig. 4 graphically presents temperature profiles for cDNA production using native and recombinant RTs (Fig. 4A), temperamre profiles of nRT and rRT catalyzing RT-PCR (Fig. 4B), temperature profiles for RT-mediated RAMP (Fig. 4C), pH profiles for nRT and rRT in RT assays (Figs. 4D and 4E), magnesium ion profile for nRT and rRT in RT assays (Fig. 4F), and other divalent cation profiles for nRT and rRT in RT assays (Fig. 4G).
- Fig. 5 illustrates the relative DNA-dependent DNA polymerase activities of native RT and recombinant RT.
- Fig. 6 shows a graphic comparison of the relative RNase activities of native RT and recombinant RT at 37 °C (Fig. 6A);
- Fig. 6B shows a temperature profile for the RNase H activity of rRT.
- the present invention provides truncated reverse transcriptase polypeptides (i.e. , fragments), and analogs and variants thereof.
- these polypeptides exhibit improved levels of RNA-dependent DNA polymerase activity, frequently extending over a wide range of temperatures up to 70°C and beyond.
- internally or terminally truncated polypeptides having sequences compatible with improved levels of expression.
- a preferred polypeptide according to the invention has a temperature optimum of 45°-55°C.
- a polypeptide consisting of an amino acid sequence set forth in SEQ ID NO:2, SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:39, SEQ ID NO:41, or SEQ ID NO: 43.
- polypeptides correspond to C-terminal truncated forms of avian reverse transcriptases, such as the full-length Myelogenetic Avian Virus-Reverse Transcriptase (i.e. , MAV-RT).
- a preferred polypeptide of the invention lacks an effective integrase catalytic activity and is expressed at elevated levels, providing a source of soluble, and recoverable, polypeptide in active form.
- Exemplary integrase domains include a Type I domain (nucleotides 2464-3012 of SEQ ID NO: 40).
- a Type II domain (nucleotides 1840-2708 of SEQ ID NO:42) and a Type III domain ((nucleotides 1734-2571 of SEQ ID NO: l), any of which may be modified by internal or terminal deletion(s) or by substitution or chemical modification.
- integrase and RT function sequentially in the viral life cycle, it is possible that RT and integrase act in a complex.
- the added functions of nucleic acid binding and polymerization provided by the integrase domain of avian RTs may result in increased processivity and superior performance of such RTs.
- non-native chimeric polypeptides of the invention further include the C-terminal addition of a polymerizing domain, such as a plurality of the same, or different, amino acids.
- a polymerizing domain such as a plurality of the same, or different, amino acids.
- Non-native chimeric polypeptides are herein defined as polypeptides not found in nature. Thus, if the parts of the chimera are found in nature, they are not found in the same relationship as exists in the non-native chimeric polypeptide.
- Preferred C-terminal amino acid additions are basic amino acids, such as histidine, lysine and arginine. These preferred C-terminal additions may promote polymerization by, e.g.
- the basic amino acids also may provide or enhance the nucleic acid binding capacity of the polypeptide.
- a preferred number of C-terminal amino acid additions is 4-50, more preferably six amino acids.
- one or more cysteine residues may be added to the C-terminus of the polypeptide.
- Other alternatives are C-terminal peptides of 4-50 amino acids having a polymerizing capacity or a DNA binding capacity, and preferably both capacities.
- the polypeptides may also have DNA-dependent DNA polymerase activities or RNase H activity.
- the invention also comprehends polypeptide variants, which have substantially the same amino acid sequence as one of the polypeptides described above. “Substantially the same” means that the sequence of the polypeptide may be aligned with one of the sequences disclosed herein, using any of the approaches known in the art (e.g. , DNASIS, Hitachi Software Engineering America, Ltd. , San Bruno, CA) such that the sequences are at least 90%, and preferably 95% or 98% , similar throughout the aligned region.
- the invention contemplates the conservative substitution of asparagine for aspartate at any one or more of amino acid positions 450, 505, or 564 of SEQ ID NO:2 to produce variant MAV-RT polypeptides lacking RNase H activity; that same substitution at any one or more of amino acid positions 497, 552, or 603 of SEQ ID NO:43 produces variants of HIV-RT polypeptides lacking RNase H activity.
- Other residues which may be changed by conservative substitution to generate RNase H " variants of MAV-RT include amino acid positions 484, 549, and 572 of SEQ ID NO:2. More generally, the invention comprehends polypeptides having substantially the same amino acid sequences, regardless of whether the differences involve conservative substitutions or not.
- residues identified above may be changed in a non-conservative manner.
- residues known to be involved in RNase H activity may be altered by substitution or deletion.
- residues include, but are not limited to, amino acids at positions 441-578 of SEQ ID NO: 2 (AMV-RT and MAV-RT; see also, RSV-RT); positions 427-1 ,055 of SEQ ID NO:39 (HIV-2-RT); positions 625-911 of SEQ ID NO:41 (MMLV-RT); and positions 427-902 of SEQ ID NO:43 (HIV-l-RT).
- polypeptide analogs which are defined herein as polypeptides that either contain known equivalents for one or more of the conventional amino acids or have been derivatized in a manner understood in the art (e.g. , glycosylation, pegylation, phosphorylation), or both.
- a preferred polynucleotide consists of the sequence set forth as SEQ ID NO: l , SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO: 10, SEQ ID NO: 11 , SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19. SEQ ID NO: 38, SEQ ID NO: 40. or SEQ ID NO: 42.
- polynucleotides substantially the same as the polynucleotides having one of the above- identified sequences are also contemplated by the invention.
- substantially the same means that the polynucleotide has a sequence that is at least 90% homologous to one of the above- described polynucleotides.
- the invention provides vectors containing at least one of these polynucleotides. Further, these vectors may be functional in prokaryotic cells, eukaryotic cells, or both cell types.
- a preferred vector is a Baculovirus vector such as pBacPak9 (Clontech Inc. Palo Alto, CA).
- the invention also provides prokaryotic and eukaryotic host cells transformed with the above-identified polynucleotides.
- a preferred host cell is an Sf9 insect cell transformed with a Baculovirus-based recombinant molecule of the invention. Other insect cell lines, such as SF21 HighFive may also be used.
- the invention provides methods of using the polynucleotides to produce RTs according to the invention.
- the polynucleotides are transformed into a prokaryotic or eukaryotic host cell under conditions that allow expression of the encoded RT polypeptide and, following an incubation period, the polypeptide is isolated.
- RT polypeptides are provided. These methods realize the benefits of speed and yield from using highly active and thermostable RT polypeptides to copy target nucleic acids (e.g. , cDNA synthesis, cDNA library construction), amplify, or sequence a target nucleic acid.
- Suitable amplification methodologies include, but are not limited to, PCR, RT-PCR, Inverse PCR, Multiplex PCR, SDA, Multiplex SDA, NASBA. 3SR, and RAMP.
- Suitable sequencing methodologies include the original enzymatic sequencing technology disclosed by Sanger and co-workers, or any of the numerous variations of that technique that have been developed since that disclosure.
- Example 1 describes the cloning of a coding region encoding the full-length MAV-RT;
- Example 2 describes the sequencing of the full-length MAV pol gene encoding reverse transcriptase;
- Example 3 discloses the cloning of selected polynucleotides according to the invention;
- Example 4 details the large-scale purification of the expressed recombinant RT;
- Example 5 describes SDS-PAGE and Western blot analyses of expressed proteins;
- Example 6 discloses an assay for RNA-dependent DNA polymerase activity;
- Example 7 illustrates assays characterizing the native reverse transcriptase (nRT) and recombinant reverse transcriptase (rRT) in terms of optima for temperature, pH, MgCl 2 , and other divalent cation concentrations;
- Example 8 discloses use of RTs in methods for copying and/or amplifying target nucleic acids;
- Example 9 describes a DNA-dependent DNA polymerase assay used to characterize nRT
- Example 1 The pol gene of MAV, encoding the full-length RT precursor polypeptide, was cloned from pMAV, a pBR322 derivative containing the pol, gag and partial env gene of MAV. Data derived from a partial restriction map of the insert fragment of pMAV is shown in Table I. Based on the map data, i pol coding region, along with some 5' and 3' non-coding sequences, was excised and ligated into several prokaryotic and eukaryotic vectors, as described below. Several recombinants were obtained from these vectors. Anti-RT monoclonal antibodies were used to analyze the expression of RT (see Example 5).
- an "ATG” was added 5' to the natural "ACT" start codon in order to allow efficient expression of the protein in prokaryotes and eukaryotes (ATG ACT GTT GCG CTA CAT CTG GCT ATT CCG CTC AAA TGG AAG CCA AAC CAC ACG CCT GTG TGG ATT TTC CAG TGG CCC, etc. ; compare the sequences provided in SEQ ID NOs 2 and 3).
- Construction of Prokaryotic Recombinant Vectors pH contains a strong and tightly regulated lambda P R promoter, a temperature sensitive ⁇ cl repressor, an E. coli origin of replication, and Amp r for selection.
- the ligation mix was incubated at 16°C for 2-4 hours.
- the ligated mix was transformed into electro-competent E.coli cells in 1 mm cuvettes using a BioRad electroporator at 1.8 KeV and 200 ohms.
- the transformed cells were plated on LB-ampicillin plates and single colonies were picked for overnight growth and mini-prep analyses.
- the recombinants were then confirmed by sequence analyses. Subsequently, the 5' noncoding regions of selected recombinants were removed by site- directed mutagenesis where appropriate.
- the pH vector containing the full-length RT gene was named pHS ⁇ Ml and the vector having the 5' non-coding region deleted was called pHS ⁇ MU ⁇ 33 (i.e. , pHRT).
- the RT protein was expressed and analyzed by SDS-PAGE and RT assays were performed as described in Examples 5 and 6.
- Other prokaryotic vectors were also successfully used (e.g. , pET21d and pTZ18U, which have the T7 promoter and the lacZ promoter, respectively). Construction of Eukaryotic Recombinant Transfer Vectors
- a baculovual expression system consisting of a transfer vector, a wild-type virus AcMNPV (Autogiaphd cahfornica nucleai polyhediosis virus) oi a derivative of ACMNPX (/ e , BacPak ⁇ (Clontech Inc )) was used to obtain recombinant transfer vectors containing the RT gene
- transfer vector pBacPak9 was used to generate recombinant molecules in accordance with the invention, such as pMBacRT, pBacMIBA, pBacMIKA, pBacMIBAhis and pBacMIKAhis (see below)
- recombinant molecules containing exogenous and typically foreign RT coding regions, were used to introduce the sequence into the viral genome for expression and propagation
- Vector pBacPak9 has a strong polyhedron promoter which is induced in insect cells late in the replication cycle of the virus Hence, foreign genes, including lethal genes, expressed with this late promoter are not toxic to the growing cell
- the polyhedron gene is not necessary for the maintenance of the virus and was therefore replaced by the foreign gene (i e , MAV-RT pol gene)
- pMBacRT the RT gene is flanked by viral DNA sequences of BacPak ⁇ , a derivative of AcMNPV
- pMBacRT was introduced into insect cells along with BacPak ⁇ DNA, the plasmid recombined with the BacPak ⁇ DNA to yield recombinant, infectious progeny virus (Ml-5 and Ml-6, collectively Ml-5, 6) containing the RT gene
- Example 2 A primer walking sequencing strategy implementing Sanger's enzymatic sequencing technique was used to confirm the sequence of the MAV-RT pol gene.
- the sequencing template was the insert of pHSEMl .
- Primers were designed to be homologous or complementary to an end of a previously determined sequence. These primers were then used to progressively extend the identification of pol gene sequence until the sequence of the entire coding region had been determined.
- the polynucleotide sequence of the MAV-RT gene and the flanking sequences are set forth as SEQ ID NO: l . Amino acid sequences encoded thereby are set forth in SEQ ID NO:2.
- 2,498 bp codes for the beta fragment (nucleotides 253-2751 of SEQ ID NO: 1) of MAV-RT; the alpha fragment of MAV-RT is encoded by nucleotides 253-1990 of SEQ ID NO: 1.
- These coding regions are expected to encode polypeptides containing amino acids 1-895 of SEQ ID NO: 2 (full- length RT; see also SEQ ID NO:3), amino acids 1-833 of SEQ ID NO:2 ( ⁇ -like polypeptide; see also, SEQ ID NO:5) and amino acids 1-579 of SEQ ID NO:2 ( ⁇ -like polypeptide; see also, residues 1-578 of SEQ ID NO:4).
- the ⁇ -like polypeptide is a fragment of the native MAV-RT ⁇ polypeptide.
- the ⁇ -like polypeptide is larger than the native MAV-RT ⁇ polypeptide and smaller than the native MAV-RT ⁇ polypeptide, with the native ⁇ polypeptide sequence extending from the N-terminus of the ⁇ -like polypeptide.
- the ⁇ -like and ⁇ -like polypeptides are referred to as the ⁇ and ⁇ polypeptides, respectively.
- Example 3 As described in Example 1 , plasmids pHSEMl and pBacRT were constructed to contain 2.95 kb and 2.81 kb inserts, respectively. These fragments contained the entire reverse transcriptase gene along with 5' and 3' non-coding regions. The 5 ' non-coding region of each construct was then removed by site-directed mutagenesis, a well-known technique in the art. In particular, the primer FSDRT (5'-TGTACTAAGGAGGTG- TTCATGACTGTTGCGCTACAT-3' ; SEQ ID NO:20) was used with pHSEM l as a template to generate pHRT (pHSEMUE33).
- Primer RSDBAC2 (5'-GCCAGATGT- AGCGCAACAGTCATATTTATAGGTTTTTTTATTAC-3'; SEQ ID NO:21) was used with pBacRT as a template to generate pMBacRT (pBPHPC3M10, pBPHPC3Ml l , pBPHPC3M 17, or, respective!) , pMBaclO, pMBacl l and pMBacl 7).
- the full-length RT coding region was used as a starting material in constructing deletion derivatives that lacked the 3' end of the MAV-RT coding region to varying extents.
- the full-length gene MI-5.6, see below
- the 3 ' (C-terminal) deletion extending to the Kpnl site (MIKA) increased the RT expression level, as evidenced by SDS-PAGE.
- Relative to the full-length gene MI-5,6
- deletion of the region extending from the Bglll site to the 3' terminus (MIBA) increased the RT expression level, activity and solubility, as evidenced by SDS-PAGE and activity assays (see below).
- the beta fragment has an additional 254 amino acids at the C-terminus, which provides an integrase activity.
- This region of the polypeptide contributes to the insolubility of the polypeptide and reduces its recovery from cell extracts, as shown by the relative insolubility of a ( +) integrase form of RT (e.g., the MIKA gene product, see below) compared to a (-) integrase form (e.g. , the MIBA gene product). Because the integrase domain is only needed for the retroviral life cycle and not for the RNA- or DNA-dependent DNA polymerase activities, this region was deleted in MIBA ( ⁇ fragment equivalent).
- RNA-dependent DNA polymerase activity RNA-dependent DNA polymerase activity.
- Convenient restriction sites such as Bgl II (spanning nucleotides 1 ,986-1 ,991 of SEQ ID NO: l) and Kpnl (spanning nucleotides 2,745-2,750 of SEQ ID NO:l) were used to eliminate the 3' end of the coding region of the RT gene (see, Table I).
- the 3' deletion derivatives, encoding RT polypeptide fragments having C-terminal deletions, were obtained by Bglll-Ps or Kpnl-Pstl restrictions of pMBacRT and pHRT, respectively (Bglll and Kpnl sites in the MAV-RT coding region; Pstl site in the vector).
- Recombinant molecules containing the Bgl II-Pstl 3 ' terminal deletion were designated pBacMIBA and pHBRT (pH33 ⁇ BP6) and recombinant molecules containing the Kpnl-Pstl deletion were designated pBacMIKA and pHKRT (pH33 ⁇ KP5).
- the deletion derivatives pBacMIBA and pBacMIKA had approximately 1.2 and 0.4 kb deletions from the 3' end of the full-length gene (see, SEQ ID NO: l), respectively.
- the fragment bounded at its 3' end by the Bglll site (SEQ ID NO:6) was used to express an alpha fragment equivalent of RT and the fragment bounded by the Kpnl site (SEQ ID NO: 8) was used to express the beta fragment equivalent of RT (the ⁇ fragment equivalent of MIKA contained amino acids 1-832 of SEQ ID NO:2; native MAV-RT ⁇ contains amino acids 1-858 of SEQ ID NO:2).
- Recombinant viruses obtained from co-transfection with virus BacPak ⁇ and transfer vector pBacMIBA or pBacMIKA were called MIBA and M IKA, respectively.
- the constructs that deleted the integrase domain of RT were not expected to retain the DNA binding, structure stabilizing, and polymerization functions attributable to the integrase domain.
- codons specifying amino acids His were added to the 3' end of the modified RT coding regions. The basic nature of the added amino acids may have been responsible for increased binding to the negatively charged nucleic acids, enhancing the stability of the polypeptides.
- the increased binding may, in turn, have been responsible for the increase in activity found with the his-tagged RTs, relative to their untagged counterparts.
- the his tags may have contributed to the tendency of the his-tagged RTs of the invention to form polymers, perhaps through his-mediated chelation of metal ions such as Ni " ' .
- a his-tagged RT (MIBAhis) was found in homo-polymeric form (molecular weight greater than 200 kDa), as determined using non-denaturing PAGE and molecular sieve chromatography with Superose 12HR 10/30 (separation range of 1-300 kDa; Pharmacia-Upjohn).
- the invention contemplates RT polypeptides lacking an effective integrase domain, but having the capacity to bind DNA and/or polymerize.
- additional functionalities may be provided by adding, preferably at the C-terminus of the modified RT, such structures as known DNA binding domains, zinc-finger or zinc-finger-like domains, polymerization domains, acidic amino acids, basic amino acids, or one or more cysteines.
- modified RTs may be ultimately derived from avian or non-avian sources. His-tag additions to the C-termini of the RT polypeptides were achieved by recombinant expression of coding regions fusing RT coding regions to His codons.
- the fusions were constructed b> adding oligonucleotides containing 6 histidine codons at the 3' end of the RT gene using ligase, as in the case of the construction of pBacMIKAhis, or by PCR amplification with oligonucleotides that specified 6 histidine codons, as in the case of the construction of pBacMIBAhis.
- pBacMIKAhis was accomplished with oligonucleotides FNhis (SEQ ID NO:33) and RNhis (SEQ ID NO:34), each of which contained internal histidine codons and compatible Notl restriction sites at each end. Following their conventional syntheses, the oligonucleotides were annealed and ligated to the 3' terminus of RT in pBacMIKA cut with Notl.
- primers FRT SEQ ID ⁇ O:22
- MlBARSDhis SEQ ID NO:23
- MlKARSDhis SEQ ID NO:24
- the his-tag derivatives of the transfer vectors were called pBacMIBAhis and pBacMIKAhis and the viruses obtained by co-transfection of Sf9 cells with the aforementioned transfer vectors and BacPak ⁇ were called MlBAhis ((-) integrase) and MlKAhis ((+) integrase), respectively.
- Introduction of the His codons led to increased activity of the encoded polypeptides in eukaryotes, as measured by SDS-polyacrylamide gel electrophoretic analyses and RT assays (see below).
- the his-tag additions increased the stability (perhaps by providing a DNA binding site), activity, polymerization capabilities and ease of purification of RTs such as MlBAhis.
- the 5' end of the MAV pol gene was also modified. Beyond deletion of the 5' non-coding sequence of pol (see the description of pHRT and pMBaclO above), the widely recognized Met initiation codon ("ATG”) was introduced immediately upstream of the natural start codon (the Thr codon "ACT" at nucleotides 253-255 of SEQ ID NO: 1) of the MAV pol gene.
- ATG Met initiation codon
- the above-described cloning strategy reflected efforts to eliminate the integrase domain of avian RT and thereby avoid the insolubility and lethality problems associated with that protein domain.
- Deletion of 192 bp from the 3' terminus of the full- length MAV-RT gene (SEQ ID NO: 1) by terminating the coding region at the Kpnl site (Table I) produced the "MIKA” clone series.
- These clones coded for a ⁇ polypeptide that is smaller than the naturally occurring ⁇ polypeptide.
- These clones exhibited enhanced RT expression and the expressed polypeptides exhibited enhanced activity levels (compare below, the expression of Ml-5, 6 [full-lengthj to MIKA [ ⁇ polypeptide]).
- RT integrase domains or non-RT integrase domains known in the art could be attached to the (-) integrase polypeptides or attach the coding regions of these domains to the polynucleotides encoding these (-) integrase polypeptides.
- Another approach is to add amino acid tags to the (-) integrase RT polypeptides (or corresponding codons to (-) integrase polynucleotides) as disclosed herein.
- a preferred tag is a basic amino acid tag such as a His tag. As disclosed below, a His tag was attached at the C- terminus of an ⁇ polypeptide equivalent (MlBAhis). This clone exhibited relatively high levels of expression, activity and solubility.
- the invention provides avian RTs improved in terms of expression and activity levels, and in terms of solubility and ease of purification, while retaining the processivity and thermostability characteristic of avian RTs.
- the invention contemplates the construction of analogous polynucleotides and recombinant molecules encoding RT polypeptides of unnatural length from other sources, such as MMLV, HIV. RSV, ASLV, ATV, and others. Further, the invention extends to polynucleotides encoding these RTs of modified length, or full length RTs, provided that the polynucleotides additionally encode polymerizing or nucleic acid binding domains, and preferably both domains, at their 3' termini.
- polynucleotides encoding a non-avian RT of unnatural length are polynucleotides encoding an RT portion or fragment having the amino acid sequence set forth at any one of the following: positions 1-765 of SEQ ID NO: 39 (an HIV-2 RT sequence), positions 1-800 of SEQ ID NO:41 (an MMLV-RT sequence), and positions 1-625 of SEQ ID NO:43 (an HIV-1 RT sequence).
- These polynucleotide sequences have some correspondence to the sequence of the polynucleotide encoding the MAV-derived MIBA polypeptide and are expected to function in a manner analogous to polynucleotides encoding MIBA.
- a polynucleotide encoding the full-length ⁇ polypeptide of HIV-2 (SEQ ID NO:38), or encoding equivalent polypeptides from MMLV or HIV-1 (SEQ ID NO:40 or SEQ ID NO:42, respectively), along with a 3' terminal sequence encoding a polymerizing and/or nucleic acid binding domain, are also contemplated by the invention.
- the invention comprehends the polypeptides encoded by the above-described polynucleotides, as well as polypeptides that have a C-terminal polymerizing and/or nucleic acid binding domain that has been added by means other than expression.
- an RT polypeptide having a Cys residue or a His residue attached at the C-terminus by chemical condensation falls within the scope of the present invention.
- effective elimination of an integrase domain such as is found in avian RTs, may be effected by altering a suitable coding region by inserting, deleting, or substituting (transitions and/or transversions), one or more nucleotides.
- RT polypeptides that are the same length as naturally occurring RT polypeptides.
- These RT polypeptides may have the same amino acid sequence as naturally occurring RTs, provided that the RTs of the invention have a polymerizing and/or nucleic acid binding domain at their C-termini.
- RTs of the same length as natural RTs may have sequences that differ from the natural RTs, thereby effectively eliminating integrase activity.
- the RTs of the invention may also be shorter, or longer, than naturally occurring RT polypeptides.
- RT polypeptides of the invention eliminate some, or all, of the C-terminal sequence of a naturally occurring RT which, in the case of avian RTs, contains the integrase domain.
- RTs of the invention that are longer than naturally occurring RT polypeptides contain the sequence of that naturally occurring RT and, in addition, sequence of an adjacent peptide region. Additionally, these polypeptides of unnatural length may have a polymerizing and/or nucleic acid binding domain added at their C-termini.
- the RT constructs described in Example 3 were transformed into prokaryotic and eukaryotic host cells and the expression of RT polypeptides was analyzed.
- a prokaryotic host cell Escherichia coli DH5 ⁇ F', was transformed with pHRT, pHBRT or pHKRT, using a technique standard in the art.
- Cells subjected to the transformation protocol were plated on LB plates (10 g tryptone, 5 g yeast extract, 5 g NaCl, 1 ml of IN NaOH, 1.5 g agar, ddH-,0 in a total volume of 1 liter) containing 50 ⁇ g/ml ampicillin for selection of transformed host cells. Single colonies were picked, expanded in small culture (i.e.
- episomal DNAs were rapidly isolated from an aliquot of cells, and the purified DNAs were analyzed for the presence of a recombinant molecule of the expected size. Dideoxynucleotide-based sequencing of these DNAs confirmed that the first ATG (i.e. , the initiation codon) was in-frame with the remainder of the RT coding region.
- RT activity was also found when expressing both the full-length and the deletion derivatives of the MAV pol coding region from other recombinant vectors, such as pTZ18U and pET21d, that contained similar insert fragments encoding full-length or C-terminally deleted MAV-RT.
- a eukaryotic host cell suitable for use in practicing the invention is the Sf9 insect cell. Several polynucleotides were separately introduced into Sf9 cells using the Baculoviral expression system. O'Reilly et al.
- the polynucleotides i.e. , pMBacRT, pBacMIBA, pBacMIBAhis, pBacMIKA, and pBacMIKAhis
- the polynucleotides were purified by the standard alkaline lysis method, as described in Sambrook et al. , (1989).
- the DNA was then centrifuged through a CHROMA SPIN+TE-400 column (Clontech Laboratories, Inc. , Palo Alto. CA.) at 500 x g for 7 minutes in a swinging bucket rotor. (HN-SII centrifuge from IEC. Inc.) This purified DNA was then used to transform eukaryotic cells.
- Sf9 insect host cells were prepared for transformation using an established procedure.
- the Sf9 cells from an exponentially growing cell culture were initially counted using a hemocytometer and diluted to 5xl0 6 cells/ml of TNM-FH Insect Cell Medium (Product No. T-1032; Sigma Chemical Co. , St. Louis, MO.) with 10% fetal bovine serum (FBS) and antibiotics (50 units/ml nystatin, 50 units/ml penicillin, and 50 ⁇ g/ml of streptomycin). Subsequently, 1.5 ml of this culture was added to each well of several 12- well tissue-culture plates. The cells were allowed to attach to the plate for a period of 1 hour.
- the medium covering the cells was then removed and 2 ml of TNM-FH medium without serum was added.
- the serum-free medium was swirled over the cells and again the medium was removed. This process was repeated one more time to remove all traces of fetal bovine serum (i.e. , FBS) and antibiotics.
- FBS fetal bovine serum
- the cells were then incubated in TNM- FH medium for 30 minutes while the transfection mixture was prepared.
- the 50 ⁇ l transfection mixture contained 500 ng of DNA, 500 ng of Bsu36l- digested BacPak ⁇ viral DNA, and ddH 2 O.
- transfection reagent (Clontech, Inc.) and incubated at room temperature for 15 minutes to allow the transfection reagent to form a complex with the DNA, as recommended by the supplier of the transfection reagent.
- Medium covering the Sf9 cells was removed and 300-500 ⁇ l of TNM-FH medium was added to each well.
- the transfection reagent-DNA mixture was added drop-wise while gently swirling the dish. The cells were then incubated at 27 °C for 5 hours before adding 2 ml of TNM-FH medium containing 10% FBS and the antibiotics identified above. DNA-cell contact was continued at 27 °C for 60-72 hours. Medium from these plates was then collected and used as primary virus stocks.
- the viruses from the clonal stocks were used to infect insect cells and ultimately analyze RT expression in a eukaryotic environment. Based on the titer obtained from the plaque assays, an infection was set up using a ratio of 5 viruses per Sf9 cell. After 60 hours, the medium and cells were collected. The cells were pelleted, resuspended in cell lysis buffer ( 10 mM Tris HCl, pH 8.0. 50 mM NaCl, 5 % glycerol, 0.5 % Triton X-100, and protease inhibitors (50 ⁇ g/ml Benzamidine HCl. 0.
- cell lysis buffer 10 mM Tris HCl, pH 8.0. 50 mM NaCl, 5 % glycerol, 0.5 % Triton X-100, and protease inhibitors (50 ⁇ g/ml Benzamidine HCl. 0.
- Sf9 cells were initially grown in T25 tissue culture flasks under the conditions described above. Sf9 cells adhering to the T25 tissue culture flasks were gently dislodged and adapted to suspension cultures as described by King et al , 1992. These suspension cultures were expanded in spinner flasks to a volume of 1-3 liters. When the insect cells reached a density of lxlO 6 cells per ml, they were infected with a concentrated stock of recombinant viruses at a ratio of 5: 1 viruses per insect cell. A variation of a standard protocol was used to infect these cells.
- a large volume of amplified viral stock (MIBA, MIKA, MlBAhis, and MlKAhis, or M 1-5,6) was concentrated using one-half volume of 40% PEG 8000 and one-sixth volume of 5 M NaCl.
- Precipitated viruses were collected at 12,000 x g for 30 minutes using a Sorvall RC5C centrifuge (Dupont, Newtown, CT). The pelleted viruses were resuspended in lx PBS (10 mM K»PO 4 , pH 7.5, and 150 mM NaCl) at 1/20 of the culture volume and stored at - 20 C C. Before infection, the viruses were filtered through a 0.2 ⁇ filter.
- Fig. 1 results of a Western blot assay using a mixture of anti-RT monoclonal antibodies 1D8, 2E10, 6F1 , 4C4, 9H 10 and 9C2 are shown in Fig. 1 (lane 1 : prestained molecular weight markers of 123 kDa, 90 kDa, 64 kDa, 50 kDa, and 38 kDa; lane 2: native AMV-RT(nRT) ( lane 2), lane 3 : M lBAhis, and lane 4: MlKAhis.
- results further indicate that both MIBA and MIKA expressed ten-fold more RT than Ml-5, 6, which encodes full-length RT.
- M IBA was expressed at 10.000 units per liter of insect cell culture
- MIKA and Ml-5, 6 were each expressed at 1 ,000 units per liter of insect cell culture.
- M IKA expressed as well as M I BA when analyzed on Western blots active MIKA recovered from the cell pellet was ten-fold less than MIBA. Most of the expressed MIKA remained insoluble in the pellet.
- MlKAhis was expressed at 2,000 units per liter of insect cell culture and MlBAhis was expressed at 200,000-400,000 units per liter of insect cell culture.
- the Baculoviral system is preferred for expression of RT and fragments thereof.
- Recombinantly expressed polypeptides of the invention were purified using conventional protocols, with metal-affinity chromatography included for the isolation of His-tagged polypeptides.
- Host cells containing recombinant molecules i.e. M 1-5,6, M IBA. M IKA, MlBAhis and MlKAhis
- RT or fragment thereof were centrifuged and the cell pellet was solubilized in 20 ml cell lysis buffer (20 mM Tris HCl, pH 8.0, 150 mM NaCl, 0.5 % Triton X, and 5 % glycerol) per gram of cell pellet.
- the resuspended cells were sonicated with five 30-second bursts at 50% power on ice with 30 seconds of cooling between each round of sonication. Sonicated cells were then stirred at a low speed on a magnetic stirrer at 4°C for one hour to complete cell lysis. The lysed samples were centrifuged at 12,000 x g for 30 minutes. The pellet was discarded and the supernatant was subjected to column chromatography.
- RTs lacking his tags were purified according to conventional protocols, which included removal of cell debris by centrifugation and subjection of supematants to chromatographic purification procedures known in the art.
- the soluble extract containing his-tagged RTs were mixed with a commercially available Ni + ' affinity column (Ni-NTA resin from Qiagen, Inc. , Chatsworth, CA), thereby using the his tags for their known purpose of facilitating purification via metal affinity chromatography.
- the extract and affinity resin were gently rocked on ice for 1 hour in a 50 ml plastic test tube.
- the resin was then packed in a column and washed with two column volumes of wash buffer (20 mM Tris HCl, pH 8.0, 250 mM NaCl, 0.5 % Triton X-100, and 5 % glycerol) and two column volumes of buffer A (20 mM Tris-HCl, pH 8.0. 250 mM NaCl. 0.5 % Triton X- 100, 5% glycerol and 50 mM imidazole).
- wash buffer (20 mM Tris HCl, pH 8.0, 250 mM NaCl, 0.5 % Triton X-100, and 5 % glycerol
- buffer A 20 mM Tris-HCl, pH 8.0. 250 mM NaCl. 0.5 % Triton X- 100, 5% glycerol and 50 mM imidazole).
- the protein bound to the column was eluted by setting up a linear gradient from buffer A to buffer B (20 mM Tris-HCl, pH 8.0, 250 mM NaCl, 0.5% Triton x-100, 5% glycerol and 250 mM imidazole).
- Fig. 2 presents an electrophoretogram of an 8% SDS-PAGE gel stained with Coomassie Blue. The lanes of the gel shown in Fig.
- Protein concentrations were determined using the Bradford protein assay (BioRad Laboratories, Inc., Hercules, CA). Generally, the specific activity of rRT (MlBAhis) was calculated to be approximately 30,000-100,000 units/mg, which is similar to the specific activity of nRT (30-100,000 units/mg).
- Example 5 The purified rRT prepared from cultures expressing MlBAhis at 400,000 units/liter of culture, a level well beyond a commercially feasible production limit, was found to be greater than 95 % pure as judged by electrophoretic fractionation using 10% SDS-PAGE.
- the apparent molecular weight of the monomer is 60 kDa, which compares well with the calculated molecular weight of approximately 59.5 kDa.
- the recombinant protein was analyzed on a 12.5 % polyacrylamide non-denaturing gel for the presence of monomers and polymers (e.g. , dimers) using the Pharmacia Phast System.
- the protein sample was prepared in either of two ways.
- RT polypeptides having C-terminal attachments in the form of compounds capable of promoting polymer formation.
- Suitable compounds would include, but are not limited to, a plurality of basic or acidic amino acids, as well as Cys residues capable of disulfide bond formation.
- rRT was also characterized immunochemically. Monoclonal antibodies against AMV reverse transcriptase were prepared using techniques well known in the art. See Harlow et al. , Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York (1988). Briefly, spleen cells from a mouse that had been immunized with RT were fused with mouse myeloma cells to make hybridomas. These hybridomas were allowed to grow into colonies in 96-well plates; supematants from these wells were then tested to find hybridomas that appeared to make anti-RT antibodies. Further testing confirmed these results.
- a BALB/C mouse female, ten weeks old, obtained from Harlan Sprague Dawley, Madison, WI was immunized by several intraperitoneal injections with AMV-RT (Molecular Biology Resources, Inc.) using a conventional immunization schedule.
- AMV-RT Molecular Biology Resources, Inc.
- the storage buffer was removed from purified RT by diluting the enzyme in phosphate-buffered saline (PBS) and reconcentrating it using a Centricon 30 concentrator (Amicon Corp.). The concentrated RT was then diluted again in PBS and emulsified with an equal volume of an adjuvant.
- the adjuvant was complete Freund's adjuvant (Sigma Chemical Co.); for the booster injections, the Ribi Adjuvant System (Ribi Immunochem Research, Inc. Hamilton, VT) was used.
- the dose of RT was approximately 20 micrograms per injection. The injections were made over a period of eight months, with successive intervals of five weeks, four weeks, three weeks, eleven weeks, eight weeks, and three weeks. The fusion was performed five days after the final boost.
- the mouse was sacrificed and spleen cells were isolated and fused with myeloma cells (P3X63-AG8.653, ATCC CRL 1580), using procedures well known in the art. See Harlow et al. In particular, the cells were fused in 50% polyethylene glycol, resuspended in a selection medium (i.e. , HAT medium), and distributed into the wells of fourteen 96- well plates. After three weeks of growth, approximately 350 wells contained hybridoma colonies. Hybridomas making anti-RT antibodies were identified by ELISA.
- the wells of 96-well polystyrene ELISA plates were first coated with purified RT (2 micrograms RT/ml in 100 mM Tris-HCl, pH 8.5, 0.05 % NaN 3 : overnight incubation at room temperature), then washed with TBST (Tris-buffered saline, pH 8.5, 0.05 % Triton X-100) to remove excess RT.
- TBST Tris-buffered saline, pH 8.5, 0.05 % Triton X-100
- the wells were filled with 95 microliters of TBST plus 5 microliters of hybridoma culture supernatant. The plates were incubated at room temperature for two hours, then washed with TBST to remove unbound immunoglobulin.
- peroxidase-conjugated goat anti-mouse IgG (heavy-chain specific; Jackson ImmunoResearch, West Grove, PA) was diluted 5, 000-fold into TBST and added to the wells of the ELISA plates. After the wells had been incubated for one hour at room temperature, the unbound peroxidase conjugate was removed by thorough washing of the plates with TBST. Wells positive for RT were visualized colorimetrically following addition of the substrate 3-methyl-2- benzothiazolinone hydrazone/3-dimethylaminobenzoic acid/hydrogen peroxide to detect immobilized HRP. Hybridomas from positive wells were repeatedly cloned by limiting dilution until all wells with growth were ELISA-positive.
- Supematants from wells that tested positive by ELISA were further screened by irnmunoprecipitation of RT using techniques well known in the art. See Harlo et al.
- the immunoprecipitation assay relies on the presence of protein A (which binds IgG) on the surface of Staphylococcus aureus cells (SAC, Sigma Chemical Co.). Since protein A does not bind strongly to mouse IgG, a pellet of centrifuged SAC cells was first treated with rabbit anti-mouse IgG antibodies. The pellet from 10 microliters of a 10% suspension of these cells was then incubated with 50 microliters of hybridoma culture supernatant for 2 hours at room temperature. The resultant SAC cells were centrifuged.
- RT activity washed, and resuspended in diluted RT.
- the RT cell suspensions were incubated for 3 hours at 4°C and centrifuged. The resultant supematants were removed and tested for depletion of RT activity using a standard radiochemical assay.
- the form of active rRT (/ ' . e. , monomer or polymer) was confirmed using ELISA in a sandwich format with anti-RT monoclonal antibodies. Initially, monoclonal antibody was immobilized in DNA bind plates. Costar Corp. , Cambridge MA. The plate was then blocked with BSA to prevent non-specific binding. The wells were then incubated with purified rRT (i.e. , MlBAhis). Excess or unbound protein was removed by washing with phosphate-buffered saline. The wells were then incubated with the same monoclonal antibody linked to biotin for detection. If the rRT existed as a monomer, the biotin-linked monoclonal antibody should not bind to it. However, the biotin-linked monoclonal antibody did bind to the rRT, indicating that the rRT had formed a polymer.
- recombinant protein expressed from each of a variety of clones e.g. , MlBAhis
- solubilized cell pellets or protein fractions from the different chromatographic columns used in purification were subjected to SDS-PAGE.
- Samples were electrophoresed on 8% polyacrylamide gels containing 6% stacking gels, followed by Coomassie Blue R- 250 staining using standard protocols (Sambrook et al. , 1989).
- the recombinant protein was found to be greater than 95 % pure.
- host cells containing one of several recombinant DNAs i.e. , pMBacRT, pBacMIBA, pBacMIKA, pBacMIBAhis, and pBacMIKAhis
- the induced cells were pelleted at 12,000 x g for 5 minutes.
- the cell pellet was then resuspended in SDS sample buffer (Sambrook et al. , 1989) or cell resuspension buffer (20 mM Tris HCl, pH 8.0, 250 mM NaCl, 0.5 % Triton X-100. and 5% glycerol) to assess the solubility of the protein.
- Resuspended cells were pulse-sonicated three times at a setting of 3 (Virsonic 100 from Virtis Company, Inc. , Gardiner, NY) for 20 seconds each (500 mM Tris HCl, pH 6.5, 14% SDS, 30% glycerol, 9.3 % DTT. and 0.012% bromophenol blue). Small aliquots of the samples in SDS sample buffer were loaded on duplicate gels and electrophoresed. One of the duplicate gels was stained with Coomassie Blue and the other gel was used to transfer protein to a 0.2 ⁇ nitrocellulose membrane using a Bio-Rad transfer apparatus for Western blot analysis. Bio Rad Laboratories, Inc. , Hercules, CA.
- Detection of expressed protein in fractionated crude lysates was possible using specific, monoclonal anti-RT antibodies (a mixture of monoclonal antibodies 4C4, 1D8, 2E10, 6F1 , 9H10, and 9C2; Molecular Biology Resources, Inc. , Milwaukee, WI) to detect the recombinant protein.
- monoclonal anti-RT antibodies a mixture of monoclonal antibodies 4C4, 1D8, 2E10, 6F1 , 9H10, and 9C2; Molecular Biology Resources, Inc. , Milwaukee, WI
- the nitrocellulose membrane containing the transferred protein was contacted with a blocking buffer (5% casein hydrolysate, 150 mM NaCl, 10 mM Tris HCl, pH 8.0) for 30 minutes followed by incubation with a 1 : 1000 dilution of anti-RT monoclonal antibody in blocking buffer. After overnight incubation, blots were rinsed in wash buffer (10 mM Tris HCl, pH 8.0, 150 mM NaCl, 0.5 % Tween 20) and incubated with a 1 :5000 dilution of alkaline phosphatase-conjugated goat anti-mouse antibody in blocking buffer for 1 hour.
- a blocking buffer 5% casein hydrolysate, 150 mM NaCl, 10 mM Tris HCl, pH 8.0
- blots were rinsed in wash buffer (10 mM Tris HCl, pH 8.0, 150 mM NaCl, 0.5 % Tween 20) and incubated
- RT was indirectly detected by performing a colorimetric phosphatase assay using a standard substrate mixture of NBT (nitroblue tetrazolium; 75 mg/ml in dimethylformamide) and BCIP (5-bromo-4-chloro-3-indolyl phosphate, 50 mg/ml in dimethylformamide), which forms a blue precipitate when dephosphorylated by any immunologically immobilized phosphatase.
- the anti-RT antibody recognized two bands, one at approximately 61 kDa and one at 92 kDa, in the lane containing native RT.
- His-tagged RT expressed from MlBAhis alpha fragment equivalent
- MlKAhis beta fragment equivalent
- Assays were also performed to determine the intrinsic/extrinsic exonuclease, endonuclease, (i.e. , nicking) DNase, and RNase activities of the rRT.
- An assay for 3'— > 5' exonuclease activity was performed using radiolabeled Taql fragments of lambda DNA as a substrate.
- RT enzyme 0.015 ⁇ g of labeled Taql fragments of ⁇ DNA, and either 2.5 or 10 units of RT enzyme.
- One unit of RT enzyme is the amount of enzyme required to incorporate 1 nmol of dTTP into an acid- insoluble form in 10 minutes at 37°C under the stated assay conditions (see. Example 6). Each sample was incubated at 37°C for 1 hour. The reaction was terminated by the addition of 50 ⁇ l of yeast tRNA and 200 ⁇ l of 10% trichloroacetic acid. After incubation for 10 minutes on ice, the samples were centrifuged for 7 minutes in a microcentrifuge.
- the rRT was also subjected to a 5'— > 3' exonuclease assay, using radiolabeled Haelll fragments of ⁇ DNA.
- the ⁇ fragments were 5' end-labeled using 60 ⁇ Ci [ ⁇ - 33 P] dATP (2,000 Ci/mmol) and 40 units of T4 polynucleotide kinase in a conventional procedure. Sambrook et al , (1989). Except for the use of 5' end-labeled Haelll fragments as substrate, this assay was performed in accordance with the description of the 3'— > 5' exonuclease assay above.
- the purified rRT released - 0.36% of the label into an acid-soluble form, an acceptably low level of 5'— > 3' exonuclease activity.
- Double-stranded and single-stranded DNase assays were also performed using the protocol for the 3'-> 5' exonuclease assay, again with the exception of the type of labeled substrate being used.
- intact lambda DNA 0.5 ⁇ g
- 30 ⁇ Ci [ ⁇ - 3 PJ dATP 2,000 Ci/mmol
- Each assay used 0.015 ⁇ g of labeled ⁇ DNA.
- the labeled ⁇ DNA fragments were further subjected to heat denaturation (3 minutes at 100°C followed immediately by chilling on ice) to prepare the substrate. Again with the exception of the type of substrate employed, each of the DNase assays were conducted as described above in the context of the 3'— > 5' exonuclease assay.
- the purified rRT was also subjected to an endonuclease, or nicking, assay by examining the extent to which the rRT converted a supercoiled substrate in the form of pBR322 to a relaxed form, as visualized by agarose gel electrophoretic fractionation.
- the assay for endonuclease activity was performed in a final volume of 10 ⁇ l containing 50 mM Tris HCl, pH 7.6. 10 mM MgCl 2 , 1 mM ⁇ -mercaptoethanol, 0.5 ⁇ g pBR322. and 2.5, 5 or 10 units of enzyme. Each sample was incubated at 37°C for 1 hour.
- the rRT was also characterized in terms of its RNase activity.
- this assay was designed to measure general RNase activity and, specifically, not an RNase H activity.
- Substrate was prepared using run-off transcription from a T7 promoter in the presence of [ ⁇ - 3 P] UTP.
- the plasmid pPV2 (a pTZ-based vector containing a ColEl ori; an ampicillin selectable marker; T7, T3 and lac promoters; and a 695 bp insert from plum pox virus) was linearized with RvwII.
- the run-off transcription reaction was performed with 1 ⁇ g of linearized pPV2, 30 ⁇ Ci of [ ⁇ - 33 P] dATP (2,000 Ci/mmol), and 10 units of T7 RNA polymerase using a conventional procedure.
- the RNase assay was then performed in the presence of single-stranded RNA substrate (0.15 ⁇ g) and rRT (2.5, 5 or 10 units). Released label was again recovered as acid-soluble material using the TCA precipitation procedure described above. Scintillation counting showed that 1 % of the radiolabel was released, indicating an acceptably low level of RNase activity.
- RNA-dependent DNA polymerase activities of native RT and recombinant RT were compared.
- One unit of enzyme was compared in RT assays with either poly rA:dT 12 . lg (20: 1) or mRNA as substrate.
- Product quantity was determined by either glass filter precipitation or binding to DE52 filters; product quality was monitored by autoradiography of a 1.2% TBE agarose gel containing fractionated reaction products.
- the reverse transcriptase activities of the native and recombinant proteins were compared using a modification of a procedure described by Meyers et al , Biochemistry 30:7661-7666 (1991).
- the reaction mixture contained lx reaction buffer ( 50 mM Tris- HCl, pH 8.3, 40 mM KC1, 10 mM MgCl 2 ), 1 mM DTT, 0.4 mM poly rA:dT 18 , 0.5 ⁇ Ci [ ⁇ - 32 P] TTP (3,000 Ci/mmol), 0.5 mM dTTP, 1 unit of enzyme (one unit of RT enzyme is the amount of enzyme required to incorporate 1 nmol of dTTP into an acid-insoluble form in 10 minutes at 37 °C under the stated assay conditions), and ddH 2 O to 50 ⁇ l total volume.
- Reaction mixtures without enzyme were pre-incubated at 37 C C for 1 minute prior to the addition of enzyme. Reactions were then incubated at 37 °C for 20 minutes, and terminated by adding 2 ⁇ l of 0.5 M EDTA followed by applying 40 ⁇ l of each reaction mixture to separate DE52 filter membranes.
- the filters were washed three times with 5 % Na 2 HPO 4 for 5 minutes each, then rinsed with ddH 2 O followed by 95 % ethanol.
- the filters were air dried, placed in scintillation fluid, and immobilized radioactivity was quantitated. A variation of the filter assay was used to compare the quantity and quality of reaction products.
- RNA messenger RNA, 891 bp control and 7.5 kb mRNA, were obtained from GIBCO BRL, Gaithersburg, MO. The following substitutions in the assay described above were made: 1 ⁇ g of mRNA primed with 0.5 mM oligo dT 12 . lg primer, instead of poly rA:dT lg ; and mixed dNTPs (0.5 ⁇ M each of dGTP, dATP, TTP and dCTP, and 0.02 ⁇ Ci [ ⁇ - 32 P]-dATP (6,000 Ci/mmol)), instead of [ ⁇ - 32 P] dTTP. Reactions were initiated by adding 5 units of RT to the reaction mixture.
- the template was 891 nucleotides (lanes 2 and 4) or 7,500 nucleotides (lanes 1 and 3); nRT was used in reactions analyzed in lanes 3 and 4, while rRT was used in reactions analyzed in lanes 1 and 2. Both the native and recombinant RTs produced products of 891 bp and 7.5 kb, depending on the size of the mRNA template.
- RNA-dependent DNA polymerase activity of native MAV-RT and recombinant MAV-RT were compared in RT assays conducted at different temperatures.
- the relative RT activities of the enzymes were compared between 37 °C and 70 °C at pH 8.0.
- the activity assays were performed in a 50 ⁇ l reaction mixture, containing 50 mM Tris HCl, pH 8, 40 mM KC1, 10 mM MgCl 2 , 1.34% trehalose, 2% maltitol, 1 mM DTT, 0.5 mM poly rA:dT 18 , 0.5 mCi [ 3 H]-dTTP (70-90 Ci/mmol), 0.5 mM dTTP, 5 U enzyme (rRT or nRT), and ddH 2 O. Duplicate reactions were incubated at each temperature for 10 minutes.
- nRT and rRT i.e. , MlBAhis
- RAMP reactions were conducted as described in PCT/US97/04170, incorporated herein by reference in its entirety.
- the target nucleic acid being amplified was Cryptosporidium mRNA from one oocyte.
- this mRNA target was reverse transcribed into cDNA at different temperatures using 20 units of native RT or 15 units of recombinant RT.
- the results are presented absorbance at 450 nm as a function of temperature in degrees Celsius, as shown in Fig. 4C (hatched line: standard; closed circles: rRT (i.e. , MlBAhis)).
- the actual absorbance values at the various temperatures are shown below the figure (upper row: standard; lower row: rRT).
- pH optima pH optima
- the pH values of selected buffers were adjusted at room temperature.
- Activity assays were performed in a 50 ⁇ l reaction mixture, containing 40 mM KC1, 10 mM MgCl 2 , 1 mM DTT, 0.5 mM poly rA:dT ]8 , 0.5 mCi [ ⁇ ]-dTTP (70-90 Ci/mmol), 0.5 mM dTTP, 5 units enzyme, ddH 2 O, and 50 mM Tris-HCl (pH 6, 7, 8, 8.3, 9, or 9.5). Reactions were incubated at 37° C or 60° C for 10 minutes.
- the reaction buffer contained 50 mM Tris-HCl, pH 8.3, and MgCl 2 ranging in concentration from 0-100 mM; all other reaction components were as described in Example 7(b).
- the reactions were incubated at 37°C.
- Inco ⁇ orated [ 3 H]-dTTP was measured by scintillation counting, with the results presented as counts per minute.
- the optimum MgCl 2 concentration was found to be 5 mM for both nRT and rRT, as shown in Fig. 4F (black: rRT (i.e. , MlBAhis); gray-hatched: nRT).
- d Other divalent cation requirements
- the reaction described above in the context of determining Mg + ⁇ concentration optima was modified to determine the influence of different divalent cations on RT activity.
- the reaction buffer included 50 mM Tris-HCl, pH 8.3, and 10 mM of the chloride salt of a divalent cation (MgCl 2 , CuCl 2 , MnCl 2 , ZnCl 2 , or CaCl 2 ). Independent experiments were performed and a curve was constructed.
- Fig. 4G shows the activities of the enzymes as counts inco ⁇ orated as a function of the cation used in the reaction (black: rRT (i.e., MlBAhis); gray-hatched: nRT). As shown in Fig. 4G, maximal activity of both nRT and rRT (i.e. , MlBAhis) was achieved using magnesium as the divalent cation.
- RT-PCR consists of a pre-amplification reaction followed by an amplification reaction.
- the pre-amplification reaction involves the use of reverse transcriptase to synthesize the first strand of cDNA using a CAT (i.e. , chloramphenicol acetyltransferase) mRNA as template.
- CAT i.e. , chloramphenicol acetyltransferase
- the CAT mRNA was provided in the Superscript kit from GIBCO-BRL, and the reaction was performed according to the supplier's recommendations. Following this reaction, the RNA from the RNA-DNA hybrid was removed by RNase H to free the first strand for use as a template in a Polymerase Chain Reaction (PCR).
- the pre-amplification reaction mixture initially consisted of 50 ng of control mRNA (i.e. , CAT mRNA), 500 ng of oligo dT 12 . 18 , and ddH 2 O to bring the mixture to a total volume of 12 ⁇ l. This mixture was incubated at 70 °C for 1 minute. Subsequently, 2 ⁇ l of lOx PCR buffer, 2 ⁇ l of 25 mM MgCl 2 , 1 ⁇ l of dNTP from a combined stock solution containing 10 mM each of dGTP, dATP, TTP and dCTP, and 2 ⁇ l of 0.1 M DTT were added to the mRNA/oligo dT mixture.
- One set of reactions was incubated with 20 U of nRT and the other set of reactions was incubated with 20 U of rRT (i. e. , M 1 B Ahis) .
- One tube from each set was incubated at one of several temperatures and each reaction proceeded for one hour. The reactions were terminated by incubation at 90 °C for 2 minutes. Reactions were then cooled on ice and 1 ⁇ l of RNase H was added to each tube and incubated at 37 °C for 20 minutes.
- each reaction mixture was assembled in a thin-wall tube containing: 5 ⁇ l of lOx PCR buffer, 3 ⁇ l of 25 mM MgCl 2 , 1 ⁇ l of dNTP from a combined stock solution containing 10 mM each of dGTP, dATP, TTP and dCTP, 1 ⁇ l each of 10 ⁇ M amplification primer 1 and 10 ⁇ M amplification primer 2 as supplied in the superscript kit, 1 ⁇ l of Taq DNA polymerase and Pyrococcus woesii (i.e. , Pwo) DNA polymerase mix, (Boehringer Mannheim Corp.
- reaction products were analyzed by subjecting 5 ⁇ l of the reaction to fractionation on a 1.2% TBE agarose gel and determining the intensity of the bands, in ng of DNA, using an imager equipped with a DC40 camera and Kodak Digital Sciences IDTM software.
- the quantity of DNA synthesized by rRT was comparable to the quantity synthesized by nRT.
- a RAMP reaction was also performed using an RT according to the invention and a first strand of cDNA from a Cryptosporidium oocyte mRNA as a template, along with a nicking enzyme (i.e., BsiHKCl) and Bst DNA polymerase.
- the Bst DNA polymerase provided both polynucleotide synthesis activity and strand displacing activity.
- the reaction consisted of 35 mM K»PO , 0.7 mM Tris-HCl, pH 7.9, 1.4 mM dCTP, 0.5 mM each of dATP, dGTP and dTTP, 35 mg of Bovine Serum Albumin, 10.2 mM MgCl 2 , 3.4 mM KC1, 0.7 mM DTT, 2% Maltitol, 1.34% Trehalose, 0.5 mM of Amplification Primer 1 (5'-ACCCCATCCAATGCATGTCTCGGGTCGTAGTCT- TAACCAT-3'; SEQ ID NO:31) and Amplification Primer 2, (5'-CGATTCCGCTC- CAGACTTCTCGGGTGCTGAAGGAGTAAGG-3'; SEQ ID NO:32) and 1 % glycerol.
- Amplification Primer 1 5'-ACCCCATCCAATGCATGTCTCGGGTCGTAGTCT- TAACCAT-3'; SEQ ID NO:31
- the amount of product synthesized in each reaction was measured by a plate assay.
- the plate assay consisted of a gene-specific capture primer (5'- AAACTATGCCAACTAGAGATTGGAGGTTGTTT-3'; SEQ ID NO: 30) bound to the wells of a microtiter plate and used to capture the product.
- the captured product was then detected by an oligonucleotide (HRP-conjugated P2 Comp; SEQ ID NO:37) linked to Horse Radish Peroxidase.
- HRP was detected by a colorimetric assay standard in the art.
- the amount of product synthesized by the rRT was two-fold more than the quantity synthesized by nRT between temperatures of 55° C to 64° C, as shown in Fig. 4C.
- the difference in temperature optima between the RT assays and the amplifications may be due, in part, to the differences in the relative RNase H activities at the assessed temperatures.
- the lowest RNase H activity was seen between 60°-65°C, temperatures that also produced longer cDNA products and greater amplification of templates.
- the temperature profile of the RNase H activity of rRT is shown in Fig. 6B.
- MAV-RT has additional enzyme activities, such as DNA-dependent DNA polymerase activity.
- the DNA- dependent DNA polymerase activity was investigated using a single-stranded M13mpl8 DNA template and a sequence-specific [ ⁇ 2 P] labeled primer (i.e. , Forward Sequencing Primer or FSP; 5'-CGCCAGGGTTTTCCCAGTCACGA-3'; SEQ ID NO:29).
- the 10 ⁇ l reaction mixture contained 50 mM Tris HCl, pH 8.3, 40 mM KC1, 10 mM MgCl 2 , 20 ⁇ M of each conventional dNTP, 0.24 pmol of sequence-specific primer FSP and 800 ng of single-stranded M13mpl8 DNA template.
- rRT i.e. , MlBAhis
- nRT a commercially av ailable thermostable DNA polymerase
- the DNA-dependent DNA polymerase activity was also determined at different temperatures. For these reactions, inco ⁇ orated [ ⁇ - 32 P]-dTTP served as a label and a non- radioactive primer was used.
- the reaction consisted of 200 ng of single-stranded M13mpl8 DNA, 1-5 pmoles of FSP, 50 mM Tris-HCl, pH 8.3, 40 mM KCl, 10 mM MgCl 2 , 1 mM DTT, 0.6 ⁇ Ci of [ ⁇ - 32 P]-dTTP (3,000 Ci/mmol), and 20 ⁇ M each of dATP, dGTP, dCTP, and dTTP, in a total volume of 24 ⁇ l.
- the enzymes may be used in any of the above-mentioned variety of amplification technologies known in the art.
- the polypeptides of the invention may be used to sequence RNA or DNA targets using Sanger's enzymatic approach as originally disclosed or any one of the many variations of that technique that have been developed since that time.
- rRT i.e. , MlBAhis
- RNase H assay using a protocol known in the art. Hillenbrand et al, Nucl. Acids
- reaction mixture less enzyme, was prepared and the reaction started by the addition of enzyme. After 20 minutes of incubation at 37°C, the reaction was terminated by adding 25 ⁇ l of cold yeast tRNA as co-precipitant (10 mg/ml in 0.1 M sodium acetate, pH 5.0) followed by 200 ⁇ l of 10% trichloroacetic acid. Samples were then placed on ice for at least 10 minutes. The mixtures were centrifuged for 7 minutes at 16.000 x g in an Eppendorf microcentrifuge (Brinkman Instruments, Westburg, NY), and 200 ⁇ l of the supernatant fluid was withdrawn and counted in 5 ml of scintillation fluid.
- the RNase H activity of the rRT at different temperatures was also tested using the reaction mixture described above. The results are presented as counts per minute of released radiolabeled ribonucleotide for each of two trials, as shown in Fig. 6A (black: rRT (i.e., MlBAhis); gray-hatched: nRT). The data show that rRT had RNase H activity comparable to that of native RT. In addition, rRT activity was assessed at a variety of temperatures and the results presented in Fig. 6B showed that rRT was active over a wide range of temperatures. The optimum RNase H activity for rRT was 50°C. In contrast, RNase H activity was relatively low at temperatures of 37 °C, 60 °C and 65 °C.
- RT activity may be optimized by adjusting the temperature to achieve the desired mix of activities.
- methods involving use of an RNase H activity may be performed at temperatures relatively close to the 55 °C temperature optimum for the RNase H activity of rRT.
- Methods that benefit from decreased RNase H activity such as RT-PCR and RAMP, may be performed at 60-65 °C to maintain a low level of RNase H activity.
- modified RTs include ⁇ and ⁇ polypeptides that have been terminally modified by deletion of a naturally occurring terminal region of the peptide to produce ⁇ -like and ⁇ -like fragments retaining RNA-dependent DNA polymerase activity.
- Other modified RTs according to the invention involve an ⁇ -like or ⁇ -like fragment attached at either the N- terminus, C- terminus, or both termini to one or more peptides (those peptides including simple homo-oligomeric peptides, preferably charged or bulky, and peptides containing useful functionalities such as DNA binding, metal binding, structure stabilizing and polymerizing [e.g.
- modified RTs include fragments that lack a sequence found internally in one of the native polypeptides, ⁇ or ⁇ .
- coli expression system there would be 90 rare codons (38 arginine, 23 proline, 15 isoleucine, 10 leucine and 4 serine codons) in the AMV-RT gene, all or some of which may be advantageously changed to frequent codons Changing all 90 rare codons to the frequent codons found in abundantly expressed genes could imbalance host cell metabolism, however To accommodate deleterious effects on host cell metabolism arising from modified RT expression levels that are too high, a library of clones may be constructed using, e.g., an M 13-based approach to site- directed mutagenesis involving oligonucleotide primer incorporation.
- pools of synthetic oligonucleotides each oligonucleotide designed to convert one or a few rare codons to frequent codons, and a template comprising a modified RT coding region may be used to synthesize a collection of modified RTs having a range of 1 -90 rare codon conversions
- Clones having RT activity may be isolated from this library by conventional screening techniques (e g , binding to radioactive substrate and activity assays, among others).
- Table II collects pertinent information. All constructions generated by PCR used a suitable, full-length coding region sequence as a template, such as the pol gene sequence found in Ml -5, 6.
- MIBA 1757 FMIBA Smal 253-269 (SEQ ID NO:25); 1986-1968 7 Lys codons RMIBA Lys (SEQ ID NO:49)
- MIBA Arg3, 1757 FMIBA Smal 253-269 X4 (SEQ ID NO:25); 1986-1967 3 Arg, 2 Asn, 1
- MIBA (Asp6) 1754 FMIBA Smal 253-269 (SEQ ID NO:
- MIBA (Asp4) 1748 FMIBA Smal 253-269 (SEQ ID NO: 25); 1986-1968 4 Asp codons RMIBA Asp4 (SEQ ID NO:53)
- MIBA (Asp5) 1751 FMIBA Smal 253-269 (SEQ ID NO:25); 1986-1968 5 Asp codons RMIBA Asp5 (SEQ ID NO:54)
- MIBA Glu6, 1754 FMIBA Smal 253-269 Xhol
- SEQ ID NO:25 1986-1968 6 Glu codons
- RMIBA Glu6, Xhol SEQ ID NO:57
- MIBK 620 1862 FMIBA Smal 253-269 (SEQ ID NO:25); 2112-2092 RMIBK 620 (SEQ ID NO:74)
- MIBA 1748 FMIBA Smal 253-269 (GPRP) (SEQ ID NO:25); 1986-1968 GPRP motif RMIBA GPRP (SEQ ID NO:67)
- MIBA (NSl 1796 FMIBA Smal 253-269 Xhol) (SEQ ID NO:25); 1986-1966 NSl site RMIBA NSl Xhol (SEQ ID NO:98)
- MIBA (3PPG 1763 FMIBA Smal 253-269 Xhol) (SEQ ID NO:25); 1986-1968 3 "PPG" motifs RMIBA 3PPG Xhol (SEQ ID NO: 70) Clone Approx. Oligonucleotide Added Added
- MIBA Nhis 1754 FMIBA Nhis 253-269 6 His codons Smal
- Smal Smal (SEQ ID NO:72); RMIBA 1986-1967 Xhol (SEQ ID NO:59)
- MIBA NWH 1769 FMIBA NWH 253-270 WH motif Smal
- Smal SEQ ID NO:73
- RMIBA 1986-1967 Xhol SEQ ID NO: 59
- Core domain 2155 FMIBA Smal 253-269 deletion- 3' (SEQ ID fragment 3 a NO: 25); and 2092-2112 RMIBK 620 Xhol (SEQ ID NO: 74); and F 2443-2463 Cint 731 Sail (SEQ ID 2736-2716 NO:88); RCint 830 Xhol (SEQ ID NO:90)
- Core domain 2101 FMIBA Smal 253-269 deletion- 3' (SEQ ID fragment 4a NO: 25); and 2092-2112 RMIBK 620 Xhol (SEQ ID 2497-2517 NO: 74); and F Cint 751 Sail 2736-2716 (SEQ ID NO: 89); RCint 830 Xhol (SEQ ID NO: 90)
- Core domain 2158 FMIBA Smal 253-269 deletion- 3' (SEQ ID fragment 4b NO: 25); and 2149-2169 RMIBK 640 Xhol; and F Cint 2497-2517 751 Sail (SEQ ID NO:89); 2736-2716 RCint 830 Xhol (SEQ ID NO:90)
- Core domain 2032 FMIBA Smal 253-269 deletion- 3' (SEQ ID fragment 5 a NO:25); and 2092-2112 RMIBK 620 Xhol (SEQ ID NO: 74); and F 2566-2586 Cint 771 Sail (SEQ ID 2736-2716 NO:99); RCint 830 Xhol (SEQ ID NO:90)
- Core domain 2152 FMIBA Smal 253-269 deletion- 3' (SEQ ID fragment 5 c NO: 25); and 2210-2232 RMIBK 660 Xhol; and F Cint 2566-2586 771 Sail (SEQ ID NO:99); 2736-2716
- the full-length RT coding region was truncated by deletions using conventional methodologies described above (e.g. , Example 3).
- One set of deletion derivatives l acked the 3' end of the MAV-RT coding region to varying extents.
- the 3' (C-terminal) deletion extending to the Kpnl site (MIKA; see SEQ ID NO: 8) increased the RT expression level, as evidenced by SDS- PAGE.
- This region of the polypeptide contributes to the insolubility of the polypeptide and reduces its recovery from cell extracts, as shown by the relative insolubility of a (+) integrase form of RT (e.g., the MIKA gene product, see below) compared to a (-) integrase form (e.g. , the MIBA gene product). Because the integrase domain is only needed for the retroviral life cycle and not for the RNA- or DNA-dependent DNA polymerase activities, this region was deleted in MIBA ( ⁇ -like fragment).
- MIBA ⁇ -like fragment (amino acids 1-578 of SEQ ID NO: 2) is larger than the naturally occurring fragment of MAV-RT (amino acids 1-573 of SEQ ID NO: 2).
- this deletion was expected to result in an increase in the solubility, and hence recovery, of the protein.
- a series of clones was constructed to express the MIBA and MIKA series of modified RTs, which have C-terminal deletions in order to increase the levels of expression and to stabilize the RT activity (RNA-dependent DNA polymerase activity).
- Convenient restriction sites in full-length clones such as PMBacRT and pHRT, e.g. , Bgl II (spanning nucleotides 1 ,986-1,991 of SEQ ID NO: l) and Kpnl (spanning nucleotides 2,745-2,750 of SEQ ID NO:l), were used to eliminate the 3' end of the coding region of the RT gene (see, Table I).
- the 3' deletion derivatives, encoding RT polypeptide fragments having C- terminal deletions, were obtained by Bglll-Pstl or Kpnl-Pstl restrictions of pMBacRT and pHRT, respectively (Bglll and Kpnl sites in the MAV-RT coding region; Pstl site in the vector).
- Recombinant molecules containing the Bgl H-Pstl 3' terminal deletion were designated pBacMIBA and pHBRT (pH33 ⁇ BP6) and recombinant molecules containing the Kpnl-Pstl deletion were designated pBacMIKA and pHKRT (pH33 ⁇ KP5).
- the deletion derivatives pBacMIBA and pBacMIKA had approximately 1 . 17 and 0.4 kb deletions from the 3' end of the full-length gene (see, SEQ ID NO: l), respectively.
- the fragment bounded at its 3' end by the Bglll site (SEQ ID NO:6) was used to express an alpha-like RT fragment (the ⁇ -like fragment, MIBA, contained amino acids 1-578 of SEQ ID NO:2; native MAV-RT ⁇ contains amino acids 1-572 of SEQ ID NO:2) and the - 56 - fragment bounded by the Kpnl site (SEQ ID NO: 8) was used to express a beta-like RT fragment (the ⁇ -like fragment, MIKA, contained amino acids 1-832 of SEQ ID NO:2; native MAV-RT ⁇ contains amino acids 1-858 of SEQ ID NO.2).
- Recombinant viruses obtained from co-transfection with virus BacPak ⁇ and transfer vector pBacMIBA or pBacMIKA were called MIBA and MIKA, respectively.
- a His-tag addition to the C-terminus of an RT polypeptide was achieved by recombinant expression of a polynucleotide containing an RT coding region fused in-frame to His codons.
- the fusions were constructed by adding oligonucleotides containing 6 histidine codons to the 3 ' end of the RT gene using ligase, as in the case of the construction of pBacMIKAhis, or by PCR amplification with oligonucleotides that specified 6 histidine codons, as in the case of the construction of pBacMIBAhis.
- His amino acids were expected to increase binding to the negatively charged nucleic acids, enhancing the stability of the polypeptides.
- the increased stability was expected to result in increased activity of amino-acid-tagged RTs, relative to their untagged counterparts
- His tags were expected to chelate metal ions (e.g., Ni '" ), thereby potentiating polymerization of the modified RTs.
- a His-tagged RT (MlBAhis) was found in homo-polymeric form (molecular weight greater than 200 kDa), as determined using non-denaturing PAGE and molecular sieve chromatography with Superose 12HR10/30 (separation range of 1-300 kDa; Pharmacia-Upjohn).
- the PCR product was restricted with a suitable restriction enzyme and ligated to pBacPak9 that was digested with a compatible enzyme
- the selected recombinants were sequenced to confirm addition of the appropriate tags
- DNA binding motifs of proteins may have either general affinity (i.e., non-specific binding) or sequence-specific affinity for DNA
- nucleic acid binding domains have been identified and reported to play a role in important cellular functions such as viral packaging, transcriptional and translational regulation, transport between the nucleus and cytoplasm, splicing, and stability, among others Karaya et al , J Biol Chem 266 11621- 1 1627 (1991), Burd, et al , Science 265 615-621 (1994), Weiss, et al , Biopolymers 48(2- 3) 167-180 (1998), Nassal, M , J Virol 66(7) 4107-16 (1992) Ritt, et al , Biochemistry 37 2673-81 (1998) DNA binding domains with general affinity are preferable to target - specific binding domains because of the reduced substrate specificity of modified RTs having such general binding domains
- RNA- and DNA-binding motifs such as RRRDRGRS are expected to yield similar results
- six continuous lysine residues did not increase the activity A higher number of lysine residues or correct spacing of the lysine residues may be required for enhancement of function
- the mechanism of enhancement of activity due to these tags could be due to the increased structural stability of the recombinant or stability resulting from direct or metal- mediated nucleic acid binding MIBA 2000-3000 Units/g of insect cells
- sequence-specific DNA binding proteins have a general basic region and a sequence-specific region for binding to DNA
- sequence-specific DNA binding motifs such as zinc-finger domains (e.g., TFIIIA CX2CX12HX3H) and the basic region of the bZIP family of proteins
- zinc-finger domains e.g., TFIIIA CX2CX12HX3H
- arginine-rich domains such as TRQARRNRRRWRARQR and YGRKKRRQRRRP that recognize specific RNA sequences that are also expected to enhance the activity of RT
- the N-terminus of the RT integrase domain has a zinc-fmger-like (Hx3HX23CX2C) motif This N-terminus binds zinc and has been reported to both induce proper folding of the N-terminus, to be remarkably thermostable as well Burke et al , J Biol. Chem 267 9639-44 (1992) Because the full-length MAV
- a beta-like derivative (620 amino acids) containing the zinc-finger-like motif was more active than the non-tagged alpha fragment (578 amino acids) and expressed 30,000 units per gram of cell pellet M1BK620 31,950 U/g
- Disulfide bond-forming domains i e , cysteine-rich regions
- Disulfide bond-forming domains i e , cysteine-rich regions
- Disulfide bond formation between the light and heavy chains are involved in disulfide bond formation between the light and heavy chains Hence, addition of two cysteine residues at the C-terminus was anticipated to promote dimer formation through disulfide bonding Addition of two cysteine residues enhanced the activity of the alpha-like fragment, however, 6 contiguous cysteine residues reduced the activity of the modified RT
- the GPRP (fibrin clotting) tetrapeptide is the primary polymerization pocket of the blood clotting protein fibrin This domain is exposed at the amino terminus of fibrin monomers by proteolytic cleavage of the precursor protein The domain then polymerizes by binding to complementary binding sites on other fibrinogen molecules to form clots Because peptides were being added to the C-terminus of ⁇ -like constructs, the reverse-sequence tetrapeptide, PRPG, was also examined
- D- isomers of amino acids are used in peptide tags
- D-isomers are used in generating PRPG peptides for use in preparing modified RTs of the invention IBA 2000-3000 U/g
- Histidine residues can also promote dimer formation mediated by metal ions
- Additions of different length histidine tags are contemplated MIBA 2000-3000 U/g MlBA his 50000-200000 U/g
- NSl is a DNA-binding protein produced by the minute virus of mice The protein has replicational and transcriptional functions Homo-oligomerization of NSl is required for its function and a small region, N-VETTVTTAQETKRGRJQTK-C, of NSl has been identified as the domain involved in oligomerization Pujol et al , J Virol 71 7393-7403 (1997) Addition of this peptide tag to the C-terminus of AMV-RT fragments enhanced RT activity MIBA 2000-3000 U/g
- Histidine tags can be used as metal binding domains, as explained above.
- modified RTs having C-terminal His tags were constructed and subjected to expression analyses The results, presented above, indicate that peptide tags, having metal binding capacity, enhance RT expression
- Zinc fingers also exhibit metal binding capacity and are also involved in DNA binding
- the N-terminus of the integrase domain of MAV-RT has a zinc-finger-like (Hx3HX23CX2C) motif This N-terminus binds zinc and has been reported to induce proper folding of the N-terminus
- peptide tags containing one or more zinc-finger- like domains will enhance the activity of modified RTs in which they are found 5_ C-terminal peptide tags having structure-stabilizing domains
- WEAAH WEAAH
- the "PPG" triple-helical domain is responsible for binding interactions in the structural protein collagen This motif is responsible for the structural stability and proper assembly of collagen Addition of peptides containing this motif in generating modified RTs according to the invention is expected to enhance the activity of such RTs relative to corresponding RTs lacking such peptides
- Tryptophan is a bulky amino acid and could substitute for histidine tags in providing structural stability Comparative assays showed that a domain comprising Trp residues enhanced RT activity approximately 50-fold
- the NSl domain primarily forms beta sheets and coils
- the presence of hydrophobic residues alone is not very desirable because they form beta sheets and are typically buried in the secondary structure of the protein This may affect the natural folding of domains Hence, a motif that had a mixture of coils and beta sheets was chosen for analysis Addition of this domain produced an active ⁇ -like fragment that appeared to be stable
- the leucine zipper motif is a helix-turn-helix motif which has been reported to dimerize by a coiled-coil interaction
- This defined structure of the leucine zipper is expected to enhance the stability of the alpha-like fragment in addition to providing dimerization abilities
- NhisMIBA modified RT
- His tag attached to the N- terminus of an ⁇ -like fragment
- Other RTs were modified to contain peptide tags at both termini (Nhis MIBA asp 4, Nhis MIBA asp 5, Nhis M IBA asp 6, and Nhis MIBA WH)
- Nhis MIBA expression shows that activity of RTs modified by a His tag present at either the N-terminus or the C-terminus is increased relative to untagged RTs
- Other variations such as the addition of peptide tags to both termini of an RT (e.g., an N-terminal
- His tag coupled to a C-terminal Asp-, Glu-, or Trp-His- (i.e., WH) tag are also contemplated by the invention.
- MIBA asp N-terminally modified RT
- Nhis MIBA asp RT having 6 His residues at the N-terminus and 4-6 Asp residues at the C-te ⁇ ninus
- Peptide tagging of other Type III RTs The strategies described above were also used to modify RTs from other avian sources, such as Rous Sarcoma Virus and Avian Tumor Virus.
- AMV-RT polynucleotides and polypeptides are applicable more generally to dimeric (i.e., Type II and Type III) reverse transcriptase coding regions and polypeptides, and all of these modified RTs fall within the scope of the present invention.
- Polynucleotides encoding a variety of beta-like modified RTs were constructed using the techniques described in Example 3 and expressed using the techniques described in Example 4, along with Ml-5, 6 encoding the full-length AMV-RT.
- Expression of the full- length beta fragment resulted in low levels of highly insoluble, full-length protein, in both a eukaryotic (insect cell) and a prokaryotic (E. coli) host. Because expression of the full-length beta fragment resulted in mostly insoluble protein, the native beta polypeptide was modified in an effort to increase its solubility and, hence, activity.
- One strategy for modifying the ⁇ fragment involved deletions of parts of the native ⁇ RT.
- the native beta coding region specifies 858 amino acids and the full-length ⁇ -like fragment disclosed herein consists of 832 amino acids.
- the ⁇ -like fragment lacks the 26 C-terminal amino acids of full-length native ⁇ .
- Modified RTs having C-termini between 580 and 832 ammo acids are also contemplated by the invention because both the 580- and the 620-amino-acid recombinants are soluble, and the 832- and 858-amino-acid recombinants are relatively insoluble, deletions that truncate the C-terminus to a position between 580-832 amino acids are expected to result in modified ⁇ -like polypeptides that are soluble
- the ⁇ -like polypeptide has a C-terminus at any one of positions 580-832, such as positions 620, 640, 660, 740, 780, or 800 (SEQ ID NO 2), resulting from deletions that eliminate 237, 217, 197, 1 17, 77 and 57 amino acids, respectively, relative to the full-length ⁇ RT Construction and expression of a deletion derivative specifying a modified ⁇ -like RT of 620 amino acids was accomplished as generally described in Examples 3 and
- a truncated ⁇ -like RT shows considerable activity, consistent with an increase in solubility relative to the full-length native ⁇ RT
- the invention contemplates polynucleotides having internal deletions relative to the native ⁇ gene, as well as the polypeptides encoded by polynucleotides having such internal deletions
- the central core region of the integrase domain is associated with the DNA cutting and joining properties of the native AMV-RT
- the core region of the integrase domain was deleted to varying extents (the region between amino acids 620-770, 640-770 or 660-770 of SEQ ID NO 2), e.g., MIBK Cint lacks amino acids 620-770 of SEQ ID NO 2, using conventional techniques
- the approach involved the initial construction of first polynucleotide fragments encoding C-terminally truncated ⁇ -like fragments using PCR with the full-length AMV-RT pol gene as a template (see Table II) Second fragments containing various lengths the 3 ' of the end of the pol gene (i.e., 3' fragment) were also constructed using PCR These 3' fragments encoded the C- terminal region of the integrase domain, some 3' fragments also contained part, but not all.
- the first polynucleotide fragments, or 5' fragments may encode peptide tags at their 5' ends
- the 3 " fragments may also encode peptide tags (see e.g., 3' Fragment 2a in Table II), with or without tags encoded by the 5' fragment, and these tag-encoding fragments are readily synthesized using the PCR primers disclosed herein (e.g., F Cint Xhol (SEQ ID NO:85) and R Cint 830 His Xhol (SEQ ID NO 91))
- the final step in generating constructs having internal deletions was to ligate truncated ⁇ -like coding regions to 3' fragments in proper order and orientation.
- amino acids 620-770 were deleted, thereby removing the core region of the integrase domain
- the C-terminal region of the integrase domain was then placed adjacent to the N-terminal region of that domain
- modified beta fragments have terminal peptide tags
- the invention contemplates modified RTs having internal deletions and, optionally, peptide tags at an N- terminus, a C-terminus or both termini
- the ⁇ -like modified RTs may be derived from any Type II or Type III RT, along with polynucleotides encoding them
- any of the modified RTs of the invention may be produced by any process disclosed herein or known in the art, such as in v vo synthesis, m vitro synthesis or chemical synthesis Further, any of these processes may be used to produce active polypeptides in a variety of forms, including monomers, homo-dimers or homo-multimers, hetero-dimers, and hetero- multimers, all of which are comprehended by the invention
- expression of the modified beta-like fragment M1BK620 Cint resulted in expression of a heterodimeric form of RT, suggesting that the beta-like fragment was processed as expected, to yield an ⁇ polypeptide in association with a modified ⁇ -like polypeptide
- Expression of other modified RTs of the invention such as other core domain deletions (e.g., ⁇ -like fragments lacking amino acids 620-731 , 640-771 , 640-731 , 660-771 , 660-731 , 680-771 , 680-731 , or 740-771 of
- heterodimers or other non-monomeric forms may arise from the interaction of a modified ⁇ -like polypeptide and a native ⁇ polypeptide, or from a modified ⁇ -like polypeptide and a modified ⁇ -like polypeptide, regardless of whether the polypeptides were produced by in vivo or m vitro expression, or by chemical synthesis
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Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
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JP2000593756A JP2002534125A (en) | 1999-01-15 | 2000-01-14 | Biologically active reverse transcriptase |
CA002359538A CA2359538A1 (en) | 1999-01-15 | 2000-01-14 | Biologically active reverse transcriptases |
EP00904342A EP1149170A1 (en) | 1999-01-15 | 2000-01-14 | Biologically active reverse transcriptases |
AU26117/00A AU2611700A (en) | 1999-01-15 | 2000-01-14 | Biologically active reverse transcriptases |
Applications Claiming Priority (2)
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US11609999P | 1999-01-15 | 1999-01-15 | |
US60/116,099 | 1999-01-15 |
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WO2000042199A1 true WO2000042199A1 (en) | 2000-07-20 |
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PCT/US2000/000896 WO2000042199A1 (en) | 1999-01-15 | 2000-01-14 | Biologically active reverse transcriptases |
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EP (1) | EP1149170A1 (en) |
JP (1) | JP2002534125A (en) |
AU (1) | AU2611700A (en) |
CA (1) | CA2359538A1 (en) |
WO (1) | WO2000042199A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1191102A2 (en) * | 2000-09-22 | 2002-03-27 | Roche Diagnostics GmbH | Method for producing an active heterodimeric AMV-RT in prokaryotic cells |
US20120156752A1 (en) * | 2008-04-10 | 2012-06-21 | Fermentas Uab | Production of nucleic acid |
CN108368151A (en) * | 2015-12-07 | 2018-08-03 | 生物辐射实验室股份有限公司 | Dimerization reverse transcriptase |
Citations (2)
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JPH0739378A (en) * | 1993-07-30 | 1995-02-10 | Takara Shuzo Co Ltd | Gene for reverse transcriptase |
US5668005A (en) * | 1988-01-13 | 1997-09-16 | Life Technologies, Inc. | Cloned genes encoding reverse transcriptase lacking RNASE H activity |
-
2000
- 2000-01-14 EP EP00904342A patent/EP1149170A1/en not_active Withdrawn
- 2000-01-14 AU AU26117/00A patent/AU2611700A/en not_active Abandoned
- 2000-01-14 JP JP2000593756A patent/JP2002534125A/en active Pending
- 2000-01-14 CA CA002359538A patent/CA2359538A1/en not_active Abandoned
- 2000-01-14 WO PCT/US2000/000896 patent/WO2000042199A1/en not_active Application Discontinuation
Patent Citations (2)
Publication number | Priority date | Publication date | Assignee | Title |
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US5668005A (en) * | 1988-01-13 | 1997-09-16 | Life Technologies, Inc. | Cloned genes encoding reverse transcriptase lacking RNASE H activity |
JPH0739378A (en) * | 1993-07-30 | 1995-02-10 | Takara Shuzo Co Ltd | Gene for reverse transcriptase |
Non-Patent Citations (2)
Title |
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NAOKO TANESE ET AL.: "Structural requirements for bacterial expression of stable, enzymatically active fusion proteins containing the human immunodeficiency virus reverse transcriptase", DNA, vol. 7, no. 6, 1988, pages 407 - 416, XP002137205 * |
QUILLENT, CAROLINE ET AL: "Extensive regions of pol are required for efficient human immunodeficienc virus polyprotein processing and particle maturation", VIROLOGY (1996), 219(1), 29-36, 1996, XP000608777 * |
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1191102A2 (en) * | 2000-09-22 | 2002-03-27 | Roche Diagnostics GmbH | Method for producing an active heterodimeric AMV-RT in prokaryotic cells |
EP1191102A3 (en) * | 2000-09-22 | 2002-07-03 | Roche Diagnostics GmbH | Method for producing an active heterodimeric AMV-RT in prokaryotic cells |
US6902920B2 (en) | 2000-09-22 | 2005-06-07 | Roche Diagnostics Operations, Inc. | Method for producing an active heterodimeric AMV-RT in prokaryotic cells |
EP2639300B1 (en) * | 2008-04-10 | 2017-08-09 | Thermo Fisher Scientific Baltics UAB | Production of nucleic acid |
US8580548B2 (en) * | 2008-04-10 | 2013-11-12 | Thermo Fisher Scientific Baltics, UAB | Production of nucleic acid |
US9683251B2 (en) | 2008-04-10 | 2017-06-20 | Thermo Fisher Scientific Baltics Uab | Production of nucleic acid |
US20120156752A1 (en) * | 2008-04-10 | 2012-06-21 | Fermentas Uab | Production of nucleic acid |
CN107058258A (en) * | 2008-04-10 | 2017-08-18 | 赛默飞世尔科技波罗的海Uvb公司 | A kind of reverse transcriptase and its polynucleotides of coding |
US10287614B2 (en) | 2008-04-10 | 2019-05-14 | Thermo Fisher Scientific Baltics Uab | Production of nucleic acid |
US10358670B2 (en) | 2008-04-10 | 2019-07-23 | Thermo Fisher Scientific Baltics Uab | Production of nucleic acid |
CN108368151A (en) * | 2015-12-07 | 2018-08-03 | 生物辐射实验室股份有限公司 | Dimerization reverse transcriptase |
CN108368151B (en) * | 2015-12-07 | 2022-11-15 | 生物辐射实验室股份有限公司 | Dimeric reverse transcriptase |
US11834685B2 (en) | 2015-12-07 | 2023-12-05 | Bio-Rad Laboratories, Inc. | Dimeric reverse transcriptase |
Also Published As
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CA2359538A1 (en) | 2000-07-20 |
JP2002534125A (en) | 2002-10-15 |
EP1149170A1 (en) | 2001-10-31 |
AU2611700A (en) | 2000-08-01 |
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