CN114480329B

CN114480329B - High efficiency MMLV enzyme mutants

Info

Publication number: CN114480329B
Application number: CN202011269318.1A
Authority: CN
Inventors: 蒋析文; 刘霭珊; 陆雪兰; 吴志坚
Original assignee: Guangzhou Da'an Gene Co ltd
Current assignee: Guangzhou Da'an Gene Co ltd
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2023-06-30
Anticipated expiration: 2040-11-13
Also published as: CN114480329A

Abstract

The invention provides a high-efficiency MMLV enzyme mutant, in particular to a reverse transcriptase (M-MLV) mutant library, which is constructed by a large number of screening, finally screens out reverse transcriptase mutants with multiple mutation sites, which have improved heat stability and higher amplification efficiency, and has obviously improved reverse transcription efficiency compared with wild M-MLV enzyme.

Description

High efficiency MMLV enzyme mutants

Technical Field

The invention belongs to the technical field of biology, and particularly relates to a high-efficiency MMLV enzyme mutant.

Background

Murine leukemia reverse transcriptase (M-MLV) is a DNA polymerase with RNA as template, has RNase H activity and no 3'-5' exonuclease activity, and can be used for reverse transcription to synthesize cDNA. Since RNA has a more complex secondary structure, the reverse transcription efficiency of M-MLV enzyme is greatly affected. The simplest method for opening the secondary structure of RNA is to open the hydrogen bond of the secondary structure by high temperature, and RNA becomes linear single-stranded. However, the optimal reaction temperature of the wild-type M-MLV enzyme is 37℃and the stability at high temperature is decreased and the activity is decreased. Therefore, the heat stability of the M-MLV enzyme is improved through mutation, and the adaptation of the M-MLV enzyme to the reaction at high temperature is the main modification direction of the M-MLV enzyme.

The mutant engineering of M-MLV enzymes has the following pathways:

1. random mutation. Random mutagenesis of the full-length sequence or of a domain of M-MLV is then carried outAnd (5) screening. The method can screen MMLV mutant with high activity and high thermal stability, but the technical process is complex, and the mutation library capacity generated by random mutation can reach 10 ⁷ With a large number of inactive mutations, the difficulty of screening is great. (reference: arezi B Hogrefe H.Novel mutations in Moloney Murine Leukemia Virus reverse transcriptase increase thermostability through tighter binding to template-primer [ J ]].Nucleic Acids Research,2008,37(2):473-481.)

2. Site-directed mutagenesis was performed on specific active sites. The method has stronger pertinence, and improves the enzyme activity by increasing the affinity of amino acids of key active sites such as nucleic acid binding sites, metal ion binding sites and the like with substrates. However, this method lacks analysis of the overall structure of the enzyme and does not improve the stability of the enzyme as a whole. ( Reference is made to: yasukawa K, mizuno M, konishi A, et al, incrustase in thermal stability of Moloney murine leukaemia virus reverse transcriptase by site-directed mutagenesis [ J ]. Journal of Biotechnology,2010,150 (3): 299-306. )

In general, due to the complexity of the protein structure, not only the amino acids located at the active site, but even some amino acids located away from the active site may have an influence on the overall structure and performance of the enzyme, and thus there is a great uncertainty in modification of the enzyme.

Disclosure of Invention

The present invention aims to provide a reverse transcriptase mutant which is resistant to high temperature and has high reverse transcription efficiency.

In a first aspect of the invention, there is provided an M-MLV enzyme mutant that is mutated at least two (which may be two, three, four, or five) sites selected from the group consisting of: amino acid residue 446, 313, 583, 607 and 221, wherein the amino acid residue number is represented by SEQ ID NO. 1.

The amino acid sequence of the corresponding wild-type murine leukemia reverse transcriptase (M-MLV) is shown in SEQ ID NO. 1.

In another preferred embodiment, in the M-MLV enzyme mutant, the amino acid residue position 446 is mutated to Cys.

In another preferred embodiment, the M-MLV enzyme mutant has the amino acid residue position at position 313 mutated to His or Gln.

In another preferred embodiment, the M-MLV enzyme mutant has the amino acid residue position 583 mutated to Asn.

In another preferred embodiment, the M-MLV enzyme mutant has a mutation of the amino acid residue at position 607 to Lys.

In another preferred embodiment, the M-MLV enzyme mutant has the amino acid residue at position 221 mutated to Arg.

In another preferred embodiment, the amino acid sequence of the M-MLV enzyme mutant has at least about 80% homology to SEQ ID NO. 1; more preferably, it has a homology of at least about 90%; most preferably, it has a homology of at least about 95%; such as having at least about 96%, 97%, 98%, 99% homology.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 583, and at amino acid residue 313.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313 and amino acid residue 221.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 583 and at amino acid residue 446.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 583, and at amino acid residue 221.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313 and amino acid residue 446.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313 and at amino acid residue 607.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313, amino acid residue 583, and amino acid residue 221.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313, amino acid residue 583, and amino acid residue 607.

In another preferred embodiment, the M-MLV enzyme mutant is mutated at amino acid residue 313, amino acid residue 583, and amino acid residue 446.

In another preferred embodiment, the M-MLV enzyme mutant has an increased reverse transcription efficiency at high temperature (58 ℃) of 10-fold or more, preferably 20-fold or more, more preferably 30-fold or more, compared to the wild-type.

In a second aspect of the invention there is provided a polynucleotide molecule encoding an M-MLV enzyme mutant according to the first aspect of the invention.

In a third aspect of the invention there is provided a vector comprising a nucleic acid molecule according to the second aspect of the invention.

In a fourth aspect of the invention there is provided a host cell comprising a vector or chromosome according to the first aspect of the invention incorporating a nucleic acid molecule according to the second aspect of the invention.

In another preferred embodiment, the host cell is a prokaryotic cell, or a eukaryotic cell.

In another preferred embodiment, the prokaryotic cell is E.coli.

In another preferred embodiment, the eukaryotic cell is a yeast cell.

In a fifth aspect of the present invention, there is provided a method for preparing the M-MLV enzyme mutant of the first aspect of the present invention, comprising the steps of:

(i) Culturing the host cell of the fourth aspect of the invention under suitable conditions to express the M-MLV enzyme mutant; and

(ii) Isolating said M-MLV enzyme mutants.

In another preferred embodiment, the temperature at which the host cells are cultured in step (i) is from 20℃to 40 ℃; preferably from 25℃to 37℃such as 35 ℃.

In a sixth aspect of the invention, there is provided a kit comprising an M-MLV enzyme mutant according to the first aspect of the invention.

In another preferred embodiment, the kit further comprises one or more components selected from the group consisting of:

dNTPs, buffers, primers, probes, and pure water.

In a seventh aspect, the invention provides the use of an M-MLV enzyme mutant according to the first aspect of the invention in the preparation of a reverse transcription detection reagent or a reverse transcription kit.

In an eighth aspect of the present invention, there is provided a method of reverse transcription of RNA, the method comprising the steps of:

(1) Providing a sample comprising RNA;

(2) Reverse transcription reaction

Performing a reverse transcription reaction on the RNA-containing sample provided in step (1) using the reverse transcriptase mutant of the first aspect of the present invention.

In another preferred embodiment, in the step (2), the reverse transcription reaction temperature is 55℃or higher, preferably 58℃or higher.

It is understood that within the scope of the present invention, the above-described technical features of the present invention and technical features specifically described below (e.g., in the examples) may be combined with each other to constitute new or preferred technical solutions. And are limited to a space, and are not described in detail herein.

Detailed Description

The present inventors have made extensive and intensive studies to construct a reverse transcriptase (M-MLV) mutant library, and finally screened mutants having improved thermostability and higher amplification efficiency by stepwise screening. On this basis, the present invention has been completed.

Before describing the present invention, it is to be understood that this invention is not limited to the particular methodology and experimental conditions described, as such methods and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, as the scope of the present invention will be limited only by the appended claims.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. As used herein, when used in reference to a specifically recited value, the term "about" means that the value can vary no more than 1% from the recited value. For example, as used herein, the expression "about 100" includes 99 and 101 and all values therebetween (e.g., 99.1, 99.2, 99.3, 99.4, etc.).

Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein.

Reverse transcriptase

Reverse transcriptase (reverse transcriptase) is also known as RNA-dependent DNA polymerase. The enzyme takes RNA as a template, dNTPs as substrates, tRNA (mainly tryptophan tRNA) as a primer, and synthesizes a DNA single strand complementary to the RNA template, called complementary DNA (cDNA) at the 3' -OH end of the tRNA according to the base pairing principle in the 5' -3' direction.

Reverse transcriptase can be used to synthesize first strand cDNA, make cDNA probes, RNA transcription, sequencing, and reverse transcription of RNA. Common reverse transcriptases in the art include murine leukemia virus (M-MLV) reverse transcriptase and Avian Myeloblastosis Virus (AMV) reverse transcriptase.

In a preferred embodiment of the invention, the wild-type M-MLV protein of the invention has the sequence:

TLNIEDEHRLHETSKEPDVSLGSTWLSDFPQAWAETGGMGLAVRQAPLIIPLKATSTPVSIKQYPMSQEARLGIKPHIQRLLDQGILVPCQSPWNTPLLPVKKPGTNDYRPVQDLREVNKRVEDIHPTVPNPYNLLSGLPPSHQWYTVLDLKDAFFCLRLHPTSQPLFAFEWRDPEMGISGQLTWTRLPQGFKNSPTLFDEALHRDLADFRIQHPDLILLQYVDDLLLAATSELDCQQGTRALLQTLGNLGYRASAKKAQICQKQVKYLGYLLKEGQRWLTEARKETVMGQPTPKTPRQLREFLGTAGFCRLWIPGFAEMAAPLYPLTKTGTLFNWGPDQQKAYQEIKQALLTAPALGLPDLTKPFELFVDEKQGYAKGVLTQKLGPWRRPVAYLSKKLDPVAAGWPPCLRMVAAIAVLTKDAGKLTMGQPLVILAPHAVEALVKQPPDRWLSNARMTHYQALLLDTDRVQFGPVVALNPATLLPLPEEGLQHNCLDILAEAHGTRPDLTDQPLPDADHTWYTDGSSLLQEGQRKAGAAVTTETEVIWAKALPAGTSAQRAELIALTQALKMAEGKKLNVYTDSRYAFATAHIHGEIYRRRGLLTSEGKEIKNKDEILALLKALFLPKRLSIIHCPGHQKGHSAEARGNRMADQAARKAAITETPDTSTLL(SEQ ID NO.:1)

in a preferred embodiment of the invention, the codon-optimized wild-type M-MLV DNA sequence (WT) is as follows:

ACGCTGAATATCGAGGACGAACACCGTCTGCACGAAACCAGCAAGGAGCCGGACGTTAGTCTGGGTAGCACGTGGCTGAGCGATTTTCCACAAGCGTGGGCGGAAACCGGTGGTATGGGTCTCGCCGTTCGCCAAGCCCCACTCATTATCCCACTGAAAGCCACGAGCACGCCGGTGAGCATCAAGCAGTACCCGATGAGCCAAGAAGCCCGCCTCGGCATTAAACCGCATATTCAGCGTCTGCTGGACCAAGGCATTCTGGTGCCGTGCCAGAGTCCGTGGAATACGCCACTGCTCCCGGTTAAGAAGCCGGGCACCAACGATTATCGCCCGGTTCAAGACCTCCGCGAAGTGAACAAGCGCGTGGAAGATATCCATCCGACCGTGCCAAATCCGTACAATCTGCTGAGTGGCCTCCCGCCGAGTCATCAATGGTACACCGTGCTGGATCTCAAGGATGCGTTTTTCTGCCTCCGTCTGCATCCAACCAGCCAGCCACTCTTTGCGTTTGAGTGGCGCGACCCAGAAATGGGTATCAGCGGTCAACTGACGTGGACGCGTCTGCCGCAAGGCTTCAAAAACAGCCCGACGCTGTTCGATGAGGCCCTCCATCGCGATCTGGCGGATTTCCGTATCCAGCATCCAGATCTGATTCTGCTGCAGTACGTTGACGATCTGCTCCTCGCGGCCACCAGTGAACTGGATTGCCAGCAAGGTACCCGTGCGCTGCTGCAGACGCTGGGCAATCTGGGCTACCGTGCCAGCGCGAAAAAGGCGCAAATCTGCCAGAAGCAAGTTAAGTACCTCGGTTATCTGCTGAAAGAGGGTCAACGCTGGCTGACCGAGGCGCGTAAAGAGACCGTTATGGGTCAGCCAACGCCAAAGACGCCACGCCAGCTCCGCGAATTTCTGGGTACCGCCGGCTTCTGTCGTCTGTGGATTCCGGGCTTCGCGGAAATGGCGGCGCCACTCTACCCGCTGACCAAAACCGGTACCCTCTTCAATTGGGGCCCAGATCAGCAGAAGGCCTACCAAGAAATTAAACAAGCGCTGCTCACCGCGCCGGCCCTCGGTCTCCCAGATCTGACCAAACCGTTTGAGCTGTTCGTGGACGAGAAGCAAGGCTACGCCAAAGGCGTGCTGACCCAGAAACTCGGTCCATGGCGTCGTCCGGTGGCCTACCTCAGTAAGAAACTGGATCCAGTTGCGGCGGGTTGGCCGCCATGTCTCCGTATGGTGGCGGCGATTGCCGTTCTGACCAAAGACGCCGGCAAACTCACCATGGGTCAGCCGCTGGTTATTCTCGCCCCACATGCGGTGGAAGCGCTGGTTAAACAACCGCCAGACCGCTGGCTGAGCAATGCCCGCATGACCCATTATCAAGCGCTGCTGCTGGACACCGACCGCGTTCAGTTCGGTCCGGTGGTTGCGCTGAATCCAGCGACGCTGCTGCCGCTGCCAGAAGAAGGTCTGCAGCACAACTGTCTGGACATTCTGGCCGAGGCCCATGGCACCCGTCCAGATCTCACCGATCAGCCACTGCCAGACGCCGATCATACGTGGTACACCGATGGTAGTAGTCTGCTGCAAGAAGGTCAACGTAAAGCGGGTGCCGCGGTGACGACGGAAACCGAGGTGATCTGGGCCAAAGCGCTGCCAGCGGGTACCAGCGCGCAACGTGCGGAACTGATCGCGCTGACCCAAGCGCTCAAAATGGCCGAGGGCAAGAAACTCAACGTGTACACCGACAGTCGCTACGCGTTTGCGACCGCGCACATCCACGGTGAGATTTATCGCCGCCGTGGTCTGCTCACGAGCGAAGGTAAGGAGATCAAGAATAAGGACGAGATCCTCGCGCTGCTGAAAGCCCTCTTTCTGCCGAAACGTCTGAGCATCATCCATTGCCCGGGTCACCAGAAGGGCCACAGTGCGGAAGCGCGCGGTAATCGCATGGCCGATCAAGCCGCGCGCAAAGCGGCGATTACGGAAACCCCGGATACGAGCACGCTGCTG(SEQ ID NO.:2)

screening and preparation of mutants

The invention calculates the change value (DDG) of the Gibbs free energy change of the enzyme molecule after single-point mutation, thereby measuring the change of the stability of the molecule after mutation. The DDG value (Delta Delta G) is a change value of the Gibbs free energy of a molecule, energy is consumed in the process of converting a protein molecule from a normal folding state to a random curling state, the energy is a Delta G value, the Delta G value can be used for measuring the stability of the protein, and the higher the Delta G value is, the more energy is consumed for protein denaturation, the higher the temperature for the protein denaturation is, and the more stable the protein is.

The protein undergoes site-directed mutagenesis, the interaction of each amino acid changes, the delta G value changes, and the difference between the delta G value of the wild type protein and the delta G value of the mutant is the DDG value. DDG >0, indicating that the Δg value of the mutated protein is lower than that of the wild type and the protein is more unstable; DDG values <0 indicate that protein Δg values are higher after mutation than wild type and protein is more stable. Therefore, the DDG value can be used for predicting structural stability change after site-directed mutagenesis of the protein. And selecting mutation with higher DDG value from a series of mutants, constructing an MMLV protein mutation library, performing expression purification, determining the activity and the thermal stability of the mutated MMLV, and screening out single-point mutants with high activity and high thermal stability. However, due to the structural complexity of proteins, it is not possible to obtain mutants which meet the demands of practical use by prediction alone, and in most cases simulating the predicted mutants results in a significant decrease in enzyme activity.

Through a large number of screening, 6 mutation sites which can enable the M-MLV enzyme to obtain high temperature resistance and high activity are screened out by the invention as follows:

the above 6 mutation sites are combined to construct 10 MMLV mutants, and MMLV mutants with better single-point mutation performance than the above 6 are obtained.

Thus, in a preferred embodiment of the invention, the invention provides an M-MLV enzyme mutant that is mutated at least two (which may be two, three, four, or five) sites selected from the group consisting of: amino acid residue 446, 313, 583, 607 and 221, wherein the amino acid residue number is represented by SEQ ID NO. 1.

In a preferred embodiment, the M-MLV enzyme mutants of the invention are as follows:

the M-MLV enzyme mutant has an increased reverse transcription efficiency at high temperature (58 ℃) of 10-fold or more, preferably 20-fold or more, more preferably 30-fold or more, compared to the wild-type.

In a preferred embodiment, the reverse transcription efficiency test method is as follows:

total RNA was extracted from Hela cells as a template, and reverse transcription was performed according to the following system

Reacting the wild type MMLV protein and the mutant MMLV protein according to the system, and inactivating at 58 ℃ for 15 minutes and at 75 ℃ for 5 minutes; then taking the reverse transcription product, and carrying out fluorescent quantitative PCR detection according to the following system

Q-PCR procedure: 95℃for 3 minutes, (95℃for 15 seconds, 60℃for 15 seconds, 72℃for 15 seconds to read the fluorescent signal) X40 cycles.

The mutant reverse transcription efficiency was calculated as follows, based on the wild-type reverse transcriptase efficiency of 100%, compared with the wild-type reverse transcriptase reaction efficiency:

reverse transcription reaction efficiency = 100% ×2 ^(Ct _{Wild type} ^-Ct _{Mutant type} ⁾

Wherein, random primer sequence of Random 6 is as follows:

nnnnnnnn (n=a or T or G or C)

The GAPDH-PF primer sequences were as follows:

GCCTGCTTCACCACCTTCTT(SEQ ID NO.:3)

the GAPDH-PR primer sequences were as follows:

TGAACGGGAAGCTCACTGGC(SEQ ID NO.:4)

the M-MLV enzyme gene sequences of the invention may be obtained by conventional methods, such as total artificial synthesis or PCR synthesis, which may be used by those of ordinary skill in the art. One preferred synthesis method is an asymmetric PCR method. The asymmetric PCR method is to amplify a large amount of single-stranded DNA (ssDNA) by PCR using a pair of primers in unequal amounts. The pair of primers is referred to as non-limiting primer and limiting primer, respectively, in a ratio of typically 50-100:1. During the first 10-15 cycles of the PCR reaction, the amplified product is mainly double stranded DNA, but when the restriction primer (low concentration primer) is consumed, the non-restriction primer (high concentration primer) directed PCR will produce a large amount of single stranded DNA. Primers for PCR can be appropriately selected according to the sequence information of the present invention disclosed herein, and can be synthesized by a conventional method. The amplified DNA/RNA fragments can be isolated and purified by conventional methods, such as by gel electrophoresis.

The M-MLV enzyme mutants of the present invention may be expressed or produced by conventional recombinant DNA techniques comprising the steps of:

(1) Transforming or transducing a suitable host cell with a polynucleotide encoding a protein of the invention, or with a recombinant expression vector comprising the polynucleotide;

(2) Culturing the host cell in a suitable medium;

(3) The target protein is isolated and purified from the culture medium or cells, thereby obtaining the M-MLV enzyme mutant.

Methods well known to those skilled in the art can be used to construct expression vectors containing the coding DNA sequences of the M-MLV enzymes of the invention and appropriate transcriptional/translational control signals, preferably commercially available vectors: pET28. These methods include in vitro recombinant DNA techniques, DNA synthesis techniques, in vivo recombinant techniques, and the like. The DNA sequence may be operably linked to an appropriate promoter in an expression vector to direct mRNA synthesis. The expression vector also includes a ribosome binding site for translation initiation and a transcription terminator. In addition, the expression vector preferably comprises one or more selectable marker genes to provide a phenotypic trait for selection of transformed host cells.

The recombinant vector comprises in the 5 'to 3' direction: a promoter, a gene of interest and a terminator. If desired, the recombinant vector may further comprise the following elements: a protein purification tag; a 3' polynucleotide acidification signal; an untranslated nucleic acid sequence; transport and targeting nucleic acid sequences; selection markers (antibiotic resistance genes, fluorescent proteins, etc.); an enhancer; or an operator.

Methods for preparing recombinant vectors are well known to those of ordinary skill in the art. The expression vector may be a bacterial plasmid, phage, yeast plasmid, plant cell virus, mammalian cell virus, or other vector. In general, any plasmid or vector may be used as long as it is capable of replication and stability in a host.

The person skilled in the art can construct vectors containing the promoter and/or the gene sequence of interest of the present invention by means of well known methods. These methods include in vitro recombinant DNA techniques, DNA synthesis techniques, in vivo recombinant techniques, and the like.

The expression vectors of the invention may be used to transform an appropriate host cell to allow the host to transcribe the RNA of interest or to express the protein of interest. The host cell may be a prokaryotic cell such as E.coli, corynebacterium glutamicum, brevibacterium flavum, streptomyces, agrobacterium: or is lowIsoeukaryotes, such as yeast cells; or higher eukaryotic cells, such as plant cells. It will be clear to one of ordinary skill in the art how to select appropriate vectors and host cells. Transformation of host cells with recombinant DNA can be performed using conventional techniques well known to those skilled in the art. When the host is a prokaryote (e.g., E.coli), caCl may be used ₂ The treatment can also be carried out by electroporation. When the host is eukaryotic, the following DNA transfection methods may be used: calcium phosphate co-precipitation, conventional mechanical methods (e.g., microinjection, electroporation, liposome encapsulation, etc.). The transformed plant may also be transformed by Agrobacterium or gene gun, such as leaf disc method, embryo transformation method, flower bud soaking method, etc. Plants can be regenerated from the transformed plant cells, tissues or organs by conventional methods to obtain transgenic plants.

The term "operably linked" refers to the attachment of a gene of interest to be expressed by transcription to its control sequences in a manner conventional in the art.

Culturing engineering bacteria and fermenting production of target protein

After obtaining the engineered cells, the engineered cells may be cultured under appropriate conditions to express the protein encoded by the gene sequence of the present invention. The medium used in the culture may be selected from various conventional media according to the host cell, and the culture is performed under conditions suitable for the growth of the host cell. After the host cells have grown to the appropriate cell density, the selected promoters are induced by suitable means (e.g., temperature switching or chemical induction) and the cells are cultured for an additional period of time.

In the present invention, conventional fermentation conditions may be employed. Representative conditions include (but are not limited to):

(a) In terms of temperature, the fermentation and induction temperatures of the M-MLV enzyme are maintained at 25-37 ℃;

(b) The pH value in the induction period is controlled to be 3-9;

(c) In the case of Dissolved Oxygen (DO), the DO is controlled to be 10-90%, and the maintenance of dissolved oxygen can be solved by the introduction of oxygen/air mixed gas;

(d) For the feeding, the type of the feeding preferably comprises carbon sources such as glycerol, methanol, glucose and the like, and the feeding can be carried out independently or by mixing;

(e) As for the induction period IPTG concentration, conventional induction concentrations can be used in the present invention, and usually the IPTG concentration is controlled to 0.1-1.5mM;

(f) The induction time is not particularly limited, and is usually 2 to 20 hours, preferably 5 to 15 hours.

The target protein M-MLV enzyme exists in E.coli cells, host cells are collected by a centrifuge, then the host cells are broken by high pressure, mechanical force, enzymatic hydrolysis cell cover or other cell breaking methods, and recombinant proteins are released, preferably a high pressure method. The host cell lysate can be purified primarily by flocculation, salting out, ultrafiltration and other methods, and then subjected to chromatography, ultrafiltration and other purification methods, or can be directly subjected to chromatography purification.

The chromatographic techniques include cation exchange chromatography, anion exchange chromatography, gel filtration chromatography, hydrophobic chromatography, affinity chromatography, etc. Common chromatographic methods include:

1. anion exchange chromatography:

anion exchange chromatography media include (but are not limited to): Q-Sepharose, DEAE-Sepharose. If the salt concentration of the fermentation sample is high, which affects the binding to the ion exchange medium, the salt concentration is reduced before ion exchange chromatography is performed. The sample can be replaced by dilution, ultrafiltration, dialysis, gel filtration chromatography and other means until the sample is similar to the corresponding ion exchange column equilibrium liquid system, and then the sample is loaded to perform gradient elution of salt concentration or pH.

2. Hydrophobic chromatography:

hydrophobic chromatography media include (but are not limited to): phenyl-Sepharose, butyl-Sepharose, octyle-Sepharose. Sample by adding NaCl, (NH) ₄ ) ₂ SO ₄ And the salt concentration is increased in an equal mode, then the sample is loaded, and the sample is eluted by a method of reducing the salt concentration. The hetero proteins with a large difference in hydrophobicity were removed by hydrophobic chromatography.

3. Gel filtration chromatography

Hydrophobic chromatography media include (but are not limited to): sephacryl, superdex, sephadex. The buffer system is replaced by gel filtration chromatography or further purified.

4. Affinity chromatography

Affinity chromatography media include (but are not limited to): hiTrap ^TM HeparinHPColumns。

5. Membrane filtration

The ultrafiltration medium comprises: organic membranes such as polysulfone membranes, inorganic membranes such as ceramic membranes, and metal membranes. The purposes of purification and concentration can be achieved by membrane filtration.

The invention has the main advantages that:

(1) The present invention provides reverse transcriptase mutants which are resistant to high temperatures and have high reverse transcription efficiency.

(2) The reverse transcriptase mutant with high reverse transcription efficiency has obviously improved amplification efficiency compared with wild type M-MLV enzyme under the same condition, so that the detection efficiency can be obviously improved.

(3) According to the invention, multiple rounds of screening are carried out from tens of mutants, 6 single-mutation high-temperature-resistant reverse transcriptase mutants are screened, and high reverse transcription efficiency can be maintained at the reverse transcription temperature of 58 ℃. Furthermore, the reaction equilibrium can be reached within 1 minute of reaction time for 3 high temperature resistant reverse transcriptase mutants. Thus, each reverse transcriptase mutant obtained by screening according to the present invention has unexpectedly superior technical effects.

(4) The single mutation sites are combined to obtain the high-temperature-resistant reverse transcriptase mutant containing multiple mutation sites, and compared with the single mutation reverse transcriptase mutant, the high-temperature-resistant reverse transcriptase mutant containing multiple mutation sites has the advantages that the reverse transcription efficiency is further improved, and the combination of the dominant mutation sites is beneficial to improving the comprehensive performance of the M-MLV enzyme.

The present invention will be described in further detail with reference to the following examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. The following examples are not to be construed as limiting the details of the experimental procedure, and are generally carried out under conventional conditions such as those described in the guidelines for molecular cloning laboratory, sambrook.J.et al, (Huang Peitang et al, beijing: scientific Press, 2002), or as recommended by the manufacturer. Percentages and parts are by weight unless otherwise indicated. The experimental materials and reagents used in the following examples were obtained from commercial sources unless otherwise specified.

Example 1 calculation and screening of DDG values at various sites

MMLV protein sequence is input into Rosetta algorithm software Cyrus Standard (Cyrus Biotechnology), and the DDG value of full-site full mutation is calculated on amino acid segments of 0-100, 101-200, 201-300, 301-400, 401-500, 501-600 and 601-671 to obtain mutation site information of obviously reduced DDG value (DDG value < -2):

TABLE 1

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EXAMPLE 2 construction of MMLV mutant library

Based on the above protein sequences, codon optimization was performed by Suzhou Jin Weizhi Biotech Co., ltd, and a DNA sequence (SEQ ID NO.: 2) was compiled.

Gene synthesis was performed by Souzhou Jin Weizhi Biotechnology Co., ltd. According to the above DNA sequence, 5 '(NheI) and 3' (XhoI) restriction sites were added, the gene was cloned into vector pET28a through 5'NheI and 3'XhoI to construct plasmid WT-pET28a, recombinant plasmid DNA and glycerol bacteria containing the recombinant plasmid were prepared, site-directed mutagenesis was performed on plasmid WT-pET28a according to the mutation sites involved in example 1, and mutation libraries Mu1-pET28a to Mu40-pET28a were constructed.

EXAMPLE 3 expression and purification of MMLV mutants

The WT-pET28a, mu 1-40-pET 28a plasmid is transformed into BL21 (DE 3) competent cells to obtain 37 expression host bacteria, then 3ml LB culture medium is transferred, shake culture is carried out for 5 hours at 37 ℃, and then 0.1Mm IPTG is added for induction culture at 18 ℃ overnight. After the induction, the cells were collected, and the lysate (50 mM Tris, 50mM NaCl, pH 7.5) was added thereto, followed by ultrasonic lysis and centrifugation to separate the supernatant. Collecting supernatant, purifying with Ni NTA metal ion chelating filler to obtain wild type and 40 mutant MMLV proteins

EXAMPLE 4 screening of mutants

A: first round of screening (screening for mutations that remain active)

Wild-type and 36 mutant MMLV proteins were reacted according to the above system, inactivated at 42℃for 15 min and at 75℃for 5 min. Then taking the reverse transcription product, and carrying out fluorescent quantitative PCR detection according to the following system

The results of fluorescent quantitative PCR for each mutant reverse transcription product are shown in the following table:

TABLE 2

The 14 mutants with underlined ct values were lower than the wild type, i.e. the reverse transcription efficiency was higher than the wild type. These mutants were selected for a second round of screening

B: second round of screening (screening high temperature resistant mutation)

Selecting the mutants selected in the first round, increasing the reverse transcription reaction temperature to 50, 55 and 58 ℃ according to the reverse transcription reaction system selected in the first round, and then detecting the reverse transcription efficiency according to the fluorescent quantitative PCR system selected in the first round, wherein the result is as follows:

TABLE 3 Table 3

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Remarks: the mutant reverse transcription efficiency was calculated as follows, based on the wild-type reverse transcriptase efficiency of 100%, compared with the wild-type reverse transcriptase reaction efficiency:

From the second round of screening, mu_15, 16, 26, 36, 38, 40,6 mutants were reverse transcribed at 58℃with a reverse transcription efficiency of not less than 50 ℃. These 6 mutants were selected for the third round of screening.

C: third round of screening (screening for high synthetic rate mutations)

Selecting the mutant selected in the second round, carrying out reverse transcription efficiency detection according to the reverse transcription reaction system selected in the first round, wherein the reverse transcription reaction temperature is 55 ℃, the reaction time is 1 minute, 2 minutes and 5 minutes, and then carrying out reverse transcription efficiency detection according to the fluorescent quantitative PCR system selected in the first round, and the result is as follows:

TABLE 4 Table 4

Group of	1min/ct mean	2min/ct mean	5min/ct mean
				WT	24.88	22.99	21.85
15	22.24	20.28	19.17
				16	20.01	19.25	19.47
26	21.17	20.79	17.72
				36	17.64	17.92	17.93
38	21.15	20.73	20.14
				40	18.95	19.00	18.34

From the results of the third round of screening, mu_16, 36, 40 reverse transcription reactions were not significantly different from 1 minute to 5 minutes, confirming that the reaction was equilibrated after 1 minute.

Example 5

In the above examples, 6 mutation sites that allow the M-MLV enzyme to attain high temperature resistance and high activity were selected as follows:

in this example, 10 MMLV mutants were constructed by combining the above 6 mutation sites, and MMLV mutants having better performance than the above 6 single point mutations were expected.

Mutations were performed on the wild-type MMLV protein sequence according to the mutation site design in the table below.

The wild type MMLV protein sequence is shown as SEQ ID NO. 1.

From the above protein sequences, codon optimization was performed by Suzhou Jin Weizhi biotechnology Co., ltd, and a DNA sequence was compiled, and a wild type MMLV DNA sequence (WT) was shown as SEQ ID NO. 2.

Gene synthesis is carried out by the Souzhou Jin Weizhi biotechnology limited company according to the DNA sequence, 5 '(NheI) and 3' (XhoI) restriction enzyme cutting sites are added, the gene is cloned to a vector pET28a through 5'NheI and 3'XhoI to construct a plasmid WT-pET28a, recombinant plasmid DNA and glycerinum containing the recombinant plasmid are prepared, site-directed mutagenesis is carried out on the plasmid WT-pET28a according to the related mutation sites, and a mutation library Mu41-pET28a to Mu50-pET28a is constructed

EXAMPLE 6 expression and purification of MMLV mutants

Mu41 to Mu50-pET28a plasmids were transformed into BL21 (DE 3) competent cells to obtain 37 expression host bacteria, which were then transferred to 3ml LB medium, shake-cultured at 37℃for 5 hours, and then induced-cultured overnight at 18℃with 0.1mM IPTG. After the induction, the cells were collected, and the lysate (50 mM Tris, 50mM NaCl, pH 7.5) was added thereto, followed by ultrasonic lysis and centrifugation to separate the supernatant. Collecting supernatant, purifying with Ni NTA metal ion chelating filler to obtain 10 mutant MMLV proteins

EXAMPLE 7 comparison of Heat resistance of 10 mutant enzymes with Single Point mutant MMLV

Mu41 to Mu50 mutant enzyme proteins at a concentration of 200U/ul and mu_15, 16, 26, 36, 38, and 40 total 6 MMLV mutant enzyme proteins were taken, placed in a constant temperature metal bath at 50℃for 60 minutes while heating on a constant temperature metal bath at 50℃at 55℃at 60℃at 65℃and 70℃for 15 minutes, and then subjected to a reverse transcription reaction together with the enzyme sample which was not subjected to the heat treatment. Total RNA is extracted from Hela cells as a template, and the reverse transcription reaction system is as follows:

inactivating at 42 ℃ for 15 minutes and at 95 ℃ for 5 minutes. Then taking the reverse transcription product, and carrying out fluorescent quantitative PCR detection according to the following system

The results of fluorescent quantitative PCR (Ct values) are shown in the following Table:

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from the above results, it can be seen that the combined mutations mu_40 to mu_50 were more stable than the single point mutant at temperatures above 55 ℃. The reverse transcription properties of the enzyme were not substantially altered by treatment at 50℃for 1 hour.

Example 8 comparison of reaction Rate of 10 mutant enzymes with Single Point mutant MMLV

The reverse transcription reaction was carried out at 55℃for 30 seconds, 1 minute, 2 minutes and 3 minutes according to the reverse transcription reaction system of example 7, and the reverse transcription products were subjected to fluorescent quantitative PCR detection, as in example 3. The Ct value results are as follows:

from the above results, it was found that the values of ct after 1 minute of reaction were substantially not different from those of ct after 2 and 3 minutes, and therefore, it was judged that the values were balanced after 1 minute of reaction. The ct values of the 10 combined mutants are smaller than those of the single-point mutant under the same reaction time, and the combination of dominant mutation sites is proved to be helpful for improving the comprehensive performance of the M-MLV enzyme.

Example 9 use in detection of novel coronavirus nucleic acids

The present example provides the use of the selected combination mutant M-MLV enzyme in novel coronavirus (2019-nCoV) detection reagents.

The sequence of ORF1ab gene and N gene of 2019-nCoV virus is detected by adopting a fluorescent quantitative PCR method, and the sequence information of the used primers and probes is as follows:

Target 1(ORF1ab):

forward primer (F): CCCTGTGGGTTTTACACTTAA (SEQ ID NO.: 5)

Reverse primer (R): ACGATTGTGCATCAGCTGA (SEQ ID NO.: 6)

Fluorescent probe (P): 5'-FAM-CCGTCTGCGGTATGTGGAAAGGTTATGG-BHQ1-3' (SEQ ID NO.: 7)

Target 2(N):

Forward primer (F): GGGGAACTTCTCCTGCTAGAAT (SEQ ID NO.: 8)

Reverse primer (R): CAGACATTTTGCTCTCAAGCTG (SEQ ID NO.: 9)

Fluorescent probe (P): 5'-FAM-TTGCTGCTGCTTGACAGATT-TAMRA-3' (SEQ ID NO.: 10)

The preparation reaction system is as follows:

after the reaction system was prepared, the RT-PCR reaction was performed as follows: 55℃for 5 min, 95℃for 2 min, (95℃for 30 seconds; 68℃for 1 min for reading fluorescence). Times.40 cycles. The results were as follows:

the Ct differences (ΔCt) of the 5 combined mutant enzymes and the wild-type M-MLV enzyme were compared, and the fold difference in ORF1ab and N gene amplification efficiencies with the wild-type M-MLV enzyme was calculated as follows:

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the amplification efficiency of the mutant is obviously improved compared with the wild type when the amplification Ct value of the novel crown reference sample is compared with that of the wild type by combining the mutant MMLV and the wild type M-MLV enzyme. Thus, the sensitivity of detection of the novel coronavirus can be significantly improved.

All documents mentioned in this application are incorporated by reference as if each were individually incorporated by reference. Further, it will be appreciated that various changes and modifications may be made by those skilled in the art after reading the above teachings, and such equivalents are intended to fall within the scope of the claims appended hereto.

Sequence listing

<110> university of Zhongshan da An Gene Co., ltd

<120> high efficiency MMLV enzyme mutants

<130> 00007510

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<213> mouse leukemia virus (Murine leukemia virus)

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Thr Leu Asn Ile Glu Asp Glu His Arg Leu His Glu Thr Ser Lys Glu

1 5 10 15

Pro Asp Val Ser Leu Gly Ser Thr Trp Leu Ser Asp Phe Pro Gln Ala

20 25 30

Trp Ala Glu Thr Gly Gly Met Gly Leu Ala Val Arg Gln Ala Pro Leu

35 40 45

Ile Ile Pro Leu Lys Ala Thr Ser Thr Pro Val Ser Ile Lys Gln Tyr

50 55 60

Pro Met Ser Gln Glu Ala Arg Leu Gly Ile Lys Pro His Ile Gln Arg

65 70 75 80

Leu Leu Asp Gln Gly Ile Leu Val Pro Cys Gln Ser Pro Trp Asn Thr

85 90 95

Pro Leu Leu Pro Val Lys Lys Pro Gly Thr Asn Asp Tyr Arg Pro Val

100 105 110

Gln Asp Leu Arg Glu Val Asn Lys Arg Val Glu Asp Ile His Pro Thr

115 120 125

Val Pro Asn Pro Tyr Asn Leu Leu Ser Gly Leu Pro Pro Ser His Gln

130 135 140

Trp Tyr Thr Val Leu Asp Leu Lys Asp Ala Phe Phe Cys Leu Arg Leu

145 150 155 160

His Pro Thr Ser Gln Pro Leu Phe Ala Phe Glu Trp Arg Asp Pro Glu

165 170 175

Met Gly Ile Ser Gly Gln Leu Thr Trp Thr Arg Leu Pro Gln Gly Phe

180 185 190

Lys Asn Ser Pro Thr Leu Phe Asp Glu Ala Leu His Arg Asp Leu Ala

195 200 205

Asp Phe Arg Ile Gln His Pro Asp Leu Ile Leu Leu Gln Tyr Val Asp

210 215 220

Asp Leu Leu Leu Ala Ala Thr Ser Glu Leu Asp Cys Gln Gln Gly Thr

225 230 235 240

Arg Ala Leu Leu Gln Thr Leu Gly Asn Leu Gly Tyr Arg Ala Ser Ala

245 250 255

Lys Lys Ala Gln Ile Cys Gln Lys Gln Val Lys Tyr Leu Gly Tyr Leu

260 265 270

Leu Lys Glu Gly Gln Arg Trp Leu Thr Glu Ala Arg Lys Glu Thr Val

275 280 285

Met Gly Gln Pro Thr Pro Lys Thr Pro Arg Gln Leu Arg Glu Phe Leu

290 295 300

Gly Thr Ala Gly Phe Cys Arg Leu Trp Ile Pro Gly Phe Ala Glu Met

305 310 315 320

Ala Ala Pro Leu Tyr Pro Leu Thr Lys Thr Gly Thr Leu Phe Asn Trp

325 330 335

Gly Pro Asp Gln Gln Lys Ala Tyr Gln Glu Ile Lys Gln Ala Leu Leu

340 345 350

Thr Ala Pro Ala Leu Gly Leu Pro Asp Leu Thr Lys Pro Phe Glu Leu

355 360 365

Phe Val Asp Glu Lys Gln Gly Tyr Ala Lys Gly Val Leu Thr Gln Lys

370 375 380

Leu Gly Pro Trp Arg Arg Pro Val Ala Tyr Leu Ser Lys Lys Leu Asp

385 390 395 400

Pro Val Ala Ala Gly Trp Pro Pro Cys Leu Arg Met Val Ala Ala Ile

405 410 415

Ala Val Leu Thr Lys Asp Ala Gly Lys Leu Thr Met Gly Gln Pro Leu

420 425 430

Val Ile Leu Ala Pro His Ala Val Glu Ala Leu Val Lys Gln Pro Pro

435 440 445

Asp Arg Trp Leu Ser Asn Ala Arg Met Thr His Tyr Gln Ala Leu Leu

450 455 460

Leu Asp Thr Asp Arg Val Gln Phe Gly Pro Val Val Ala Leu Asn Pro

465 470 475 480

Ala Thr Leu Leu Pro Leu Pro Glu Glu Gly Leu Gln His Asn Cys Leu

485 490 495

Asp Ile Leu Ala Glu Ala His Gly Thr Arg Pro Asp Leu Thr Asp Gln

500 505 510

Pro Leu Pro Asp Ala Asp His Thr Trp Tyr Thr Asp Gly Ser Ser Leu

515 520 525

Leu Gln Glu Gly Gln Arg Lys Ala Gly Ala Ala Val Thr Thr Glu Thr

530 535 540

Glu Val Ile Trp Ala Lys Ala Leu Pro Ala Gly Thr Ser Ala Gln Arg

545 550 555 560

Ala Glu Leu Ile Ala Leu Thr Gln Ala Leu Lys Met Ala Glu Gly Lys

565 570 575

Lys Leu Asn Val Tyr Thr Asp Ser Arg Tyr Ala Phe Ala Thr Ala His

580 585 590

Ile His Gly Glu Ile Tyr Arg Arg Arg Gly Leu Leu Thr Ser Glu Gly

595 600 605

Lys Glu Ile Lys Asn Lys Asp Glu Ile Leu Ala Leu Leu Lys Ala Leu

610 615 620

Phe Leu Pro Lys Arg Leu Ser Ile Ile His Cys Pro Gly His Gln Lys

625 630 635 640

Gly His Ser Ala Glu Ala Arg Gly Asn Arg Met Ala Asp Gln Ala Ala

645 650 655

Arg Lys Ala Ala Ile Thr Glu Thr Pro Asp Thr Ser Thr Leu Leu

660 665 670

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<213> Artificial sequence (Artificial sequence)

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acgctgaata tcgaggacga acaccgtctg cacgaaacca gcaaggagcc ggacgttagt 60

ctgggtagca cgtggctgag cgattttcca caagcgtggg cggaaaccgg tggtatgggt 120

ctcgccgttc gccaagcccc actcattatc ccactgaaag ccacgagcac gccggtgagc 180

atcaagcagt acccgatgag ccaagaagcc cgcctcggca ttaaaccgca tattcagcgt 240

ctgctggacc aaggcattct ggtgccgtgc cagagtccgt ggaatacgcc actgctcccg 300

gttaagaagc cgggcaccaa cgattatcgc ccggttcaag acctccgcga agtgaacaag 360

cgcgtggaag atatccatcc gaccgtgcca aatccgtaca atctgctgag tggcctcccg 420

ccgagtcatc aatggtacac cgtgctggat ctcaaggatg cgtttttctg cctccgtctg 480

catccaacca gccagccact ctttgcgttt gagtggcgcg acccagaaat gggtatcagc 540

ggtcaactga cgtggacgcg tctgccgcaa ggcttcaaaa acagcccgac gctgttcgat 600

gaggccctcc atcgcgatct ggcggatttc cgtatccagc atccagatct gattctgctg 660

cagtacgttg acgatctgct cctcgcggcc accagtgaac tggattgcca gcaaggtacc 720

cgtgcgctgc tgcagacgct gggcaatctg ggctaccgtg ccagcgcgaa aaaggcgcaa 780

atctgccaga agcaagttaa gtacctcggt tatctgctga aagagggtca acgctggctg 840

accgaggcgc gtaaagagac cgttatgggt cagccaacgc caaagacgcc acgccagctc 900

cgcgaatttc tgggtaccgc cggcttctgt cgtctgtgga ttccgggctt cgcggaaatg 960

gcggcgccac tctacccgct gaccaaaacc ggtaccctct tcaattgggg cccagatcag 1020

cagaaggcct accaagaaat taaacaagcg ctgctcaccg cgccggccct cggtctccca 1080

gatctgacca aaccgtttga gctgttcgtg gacgagaagc aaggctacgc caaaggcgtg 1140

ctgacccaga aactcggtcc atggcgtcgt ccggtggcct acctcagtaa gaaactggat 1200

ccagttgcgg cgggttggcc gccatgtctc cgtatggtgg cggcgattgc cgttctgacc 1260

aaagacgccg gcaaactcac catgggtcag ccgctggtta ttctcgcccc acatgcggtg 1320

gaagcgctgg ttaaacaacc gccagaccgc tggctgagca atgcccgcat gacccattat 1380

caagcgctgc tgctggacac cgaccgcgtt cagttcggtc cggtggttgc gctgaatcca 1440

gcgacgctgc tgccgctgcc agaagaaggt ctgcagcaca actgtctgga cattctggcc 1500

gaggcccatg gcacccgtcc agatctcacc gatcagccac tgccagacgc cgatcatacg 1560

tggtacaccg atggtagtag tctgctgcaa gaaggtcaac gtaaagcggg tgccgcggtg 1620

acgacggaaa ccgaggtgat ctgggccaaa gcgctgccag cgggtaccag cgcgcaacgt 1680

gcggaactga tcgcgctgac ccaagcgctc aaaatggccg agggcaagaa actcaacgtg 1740

tacaccgaca gtcgctacgc gtttgcgacc gcgcacatcc acggtgagat ttatcgccgc 1800

cgtggtctgc tcacgagcga aggtaaggag atcaagaata aggacgagat cctcgcgctg 1860

ctgaaagccc tctttctgcc gaaacgtctg agcatcatcc attgcccggg tcaccagaag 1920

ggccacagtg cggaagcgcg cggtaatcgc atggccgatc aagccgcgcg caaagcggcg 1980

attacggaaa ccccggatac gagcacgctg ctg 2013

<210> 3

<211> 20

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 3

gcctgcttca ccaccttctt 20

<210> 4

<211> 20

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 4

tgaacgggaa gctcactggc 20

<210> 5

<211> 21

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 5

ccctgtgggt tttacactta a 21

<210> 6

<211> 19

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 6

acgattgtgc atcagctga 19

<210> 7

<211> 28

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 7

ccgtctgcgg tatgtggaaa ggttatgg 28

<210> 8

<211> 22

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 8

ggggaacttc tcctgctaga at 22

<210> 9

<211> 22

<212> DNA

<213> Artificial sequence (Artificial sequence)

<400> 9

cagacatttt gctctcaagc tg 22

<210> 10

<211> 20

<212> DNA

<213> Artificial sequence (Artificial sequence)

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ttgctgctgc ttgacagatt 20

Claims

1. An M-MLV enzyme mutant, wherein said M-MLV enzyme mutant is mutated at amino acid residue 313, amino acid residue 583, and amino acid residue 446; and, the 313 th amino acid residue position is mutated to Gln, the 583 rd amino acid residue position is mutated to Asn, the 446 th amino acid residue position is mutated to Cys, wherein the amino acid residue number corresponds to the number shown in SEQ ID NO. 1.

2. A polynucleotide molecule encoding the M-MLV enzyme mutant of claim 1.

3. A vector comprising the polynucleotide molecule of claim 2.

4. A host cell comprising the vector of claim 3 or a chromosome incorporating the polynucleotide molecule of claim 2.

5. The host cell of claim 4, wherein the host cell is a prokaryotic cell, or a eukaryotic cell.

6. A kit comprising the M-MLV enzyme mutant of claim 1.

7. A method of preparing the M-MLV enzyme mutant of claim 1, comprising the steps of:

(i) Culturing the host cell of claim 4 under suitable conditions to express said M-MLV enzyme mutant; and

(ii) Isolating said M-MLV enzyme mutants.

8. Use of the M-MLV enzyme mutant of claim 1 in the preparation of a reverse transcription detection reagent or a reverse transcription kit.

9. A method of reverse transcription of RNA, the method comprising the steps of:

(1) Providing a sample comprising RNA;

(2) Reverse transcription reaction:

performing a reverse transcription reaction on the RNA-containing sample provided in step (1) using the reverse transcriptase mutant of claim 1.