WO2016039377A1 - 耐熱性のミスマッチエンドヌクレアーゼの利用方法 - Google Patents
耐熱性のミスマッチエンドヌクレアーゼの利用方法 Download PDFInfo
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- C12Q2521/00—Reaction characterised by the enzymatic activity
- C12Q2521/30—Phosphoric diester hydrolysing, i.e. nuclease
- C12Q2521/301—Endonuclease
Definitions
- the present invention relates to a novel thermostable mismatch endonuclease that recognizes and cleaves a mismatched base pair in a double-stranded nucleic acid, a composition containing the mismatch endonuclease, and a method using the mismatch endonuclease.
- the analysis method of these mutations is mainly a method of directly analyzing the genome sequence, but another method using an enzyme group that recognizes mismatched base pairs has been performed.
- One of the analysis methods is to detect a mismatched base pair formed by pairing mutant and wild-type DNA by binding a factor capable of specific binding to the mismatched base pair.
- An example is a search for mutation sites using the MutS, MutT, and MutL complexes of Escherichia coli (Patent Document 1).
- a method using a mismatch endonuclease that specifically cleaves a mismatch site has been performed.
- the presence or absence of a mutation and its position are detected by analyzing a DNA fragment cleaved near the mismatched base pair using a mismatch endonuclease.
- a method using a CelI gene product derived from celery is known (Patent Document 2), and is actually used for analysis of mutant bases.
- this enzyme does not have heat resistance and cannot be used directly for techniques including high temperature reaction processes such as PCR. For this reason, when detecting a mutant base, four steps of amplification, mismatch formation, mismatch cleavage, and detection are required.
- thermostable mismatch endonuclease has been developed and is expected to be used.
- the mismatch endonuclease is characterized by recognizing GG, GT, TG, and TT mismatch sites and cleaving both strands of DNA in the vicinity thereof. (Patent Document 3)
- a biotechnological technique that has a great influence on mutation analysis is a nucleic acid amplification technique.
- the polymerase chain reaction (PCR) method which is a representative technique among the nucleic acid amplification techniques, is a technique for simply amplifying a desired nucleic acid fragment in a test tube. It is an indispensable experimental method in a wide range of fields such as academics, medicine, and agriculture.
- the PCR method is also applied to the detection of mutant genes and the analysis of DNA methylation.
- the LAMP method, the ICAN method, and the like which are isothermal nucleic acid amplification methods, are used as cheaper nucleic acid detection methods because no special equipment is required. Further, in the structure analysis of the whole genome which has been carried out in recent years, the whole genome amplification method is an important technique particularly in analyzing from a rare sample.
- DNA molecules with a high content rate are preferentially amplified in the nucleic acid amplification method, which may hinder the analysis and screening of various types of DNA.
- Non-patent Document 1 the ratio of DNA having a high content is reduced by normalization using self-hybridization.
- Non-patent Document 2 the SSH-PCR method combining the PCR method and self-hybridization is also used (Non-patent Document 2), but there is a risk that DNA having high homology with DNA is also removed.
- amplification of DNA to be detected may compete with amplification of DNA not to be detected. That is, this is a case where DNA other than the detection target is also amplified at the same time and it is difficult to detect the target DNA.
- the above problem may be solved by detecting only amplification of the DNA to be detected by real-time PCR using a probe such as a cycling probe or TaqMan probe, the DNA that is not the detection target is excessively large relative to the DNA to be detected. When it exists, it is difficult to accurately detect the DNA to be detected because of false positive reaction due to the presence of many similar DNAs.
- Such problems include, for example, detection of a small number of mutant alleles in the presence of normal alleles (such as detection of circulating tumor DNA in the blood), detection of small numbers of methylated or unmethylated alleles in epigenetic assays, This can occur in implementations such as detecting small amounts of fetal DNA sequences circulating in the mother's blood.
- Non-patent Document 3 a method called Restriction endoclease-mediate selective selective chain reaction (REMS PCR) was developed (Non-patent Document 3).
- This method uses a thermostable restriction enzyme, for example, a DNA having a mutant base sequence using a primer designed so that cleavage by this restriction enzyme occurs only when the template has a normal base sequence. This is a method of selectively detecting only.
- thermostable restriction enzyme for example, a DNA having a mutant base sequence using a primer designed so that cleavage by this restriction enzyme occurs only when the template has a normal base sequence.
- This is a method of selectively detecting only.
- there may be no thermostable restriction enzyme having a recognition sequence suitable for selective detection by REMS PCR, which lacks versatility.
- a method for avoiding a false positive reaction due to the presence of a large number of similar DNAs even when a large amount of non-detectable DNA is present relative to the DNA to be detected Is required.
- An object of the present invention is to provide a novel mismatch endonuclease, a composition containing the mismatch endonuclease, and use of the mismatch endonuclease.
- polypeptide having the enzyme activity is referred to as TKO NucS.
- thermostable mismatch endonuclease we succeeded in creating a mutant mismatch endonuclease with improved base specificity different from that of the natural type.
- the mutant mismatch endonuclease and / or the natural mismatch endonuclease It has been found that the use of a single or a combination thereof can suppress cleavage other than a specific mismatched base pair and can suppress amplification more specifically, thereby completing the present invention.
- the first invention of the present invention is a method for cleaving a double-stranded nucleic acid, wherein at least one polypeptide selected from the group consisting of the following (i) to (iii) A method characterized by acting on a strand nucleic acid and recognizing and cleaving both strands of the double-stranded nucleic acid at a GG, GT or TT mismatch base pair site: (I) a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 in the Sequence Listing; (Ii) having an amino acid sequence in which one or several amino acid residues are substituted, deleted, inserted and / or added in the amino acid sequence set forth in SEQ ID NO: 1 in the Sequence Listing, and GG, G A polypeptide having a mismatch endonuclease activity that recognizes and cleaves a T or TT mismatch; and (iii) 95% or more amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO:
- a second invention of the present invention is a composition comprising the following (a) to (c): (A) DNA polymerase; (B) at least one pair of oligonucleotide primers; and (c) at least one polypeptide selected from the group consisting of (i) to (iii) below: (I) a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 in the Sequence Listing; (Ii) having an amino acid sequence in which one or several amino acid residues are substituted, deleted, inserted, and / or added in the amino acid sequence set forth in SEQ ID NO: 1 in the Sequence Listing, and GG, G- A polypeptide having a mismatch endonuclease activity that recognizes and cleaves T or TT mismatch; and (iii) has 95% or more amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO: 1 in the sequence listing
- the present invention relates to a polypeptide having an amino acid sequence and having a mismatch endon
- a third invention of the present invention is a method for amplifying a nucleic acid, comprising the following steps (a) to (b): (A) a step of preparing a composition comprising a nucleic acid molecule as a template with the composition of the second invention of the present invention; and (b) reacting the composition obtained in step (a) under suitable conditions. And a step of performing nucleic acid amplification.
- a fourth invention of the present invention is a polypeptide selected from the group consisting of the following (A) to (C): (A) a polypeptide having the amino acid sequence set forth in SEQ ID NO: 3 in the Sequence Listing, (B) an amino acid obtained by substituting, deleting, inserting, and / or adding one or several amino acid residues except the 47th and 76th amino acid residues in the amino acid sequence of the polypeptide of (A).
- a mismatch endonuclease having a substituted amino acid sequence and recognizing and cleaving an AA, AC or CC mismatch Polypeptide having zero activity relates.
- a fifth invention of the present invention is a composition comprising the following (a) to (c): (A) DNA polymerase; (B) at least one pair of oligonucleotide primers; and (c) at least one polypeptide selected from the group consisting of (i) to (iii) below: (I) a polypeptide having the amino acid sequence set forth in SEQ ID NO: 3 in the sequence listing; (Ii) An amino acid obtained by substituting, deleting, inserting, and / or adding one or several amino acid residues except the 47th and 76th amino acid residues in the amino acid sequence of the polypeptide of (i) A polypeptide having a sequence and having a mismatch endonuclease activity that recognizes and cleaves an AA, AC or CC mismatch; and (iii) against the amino acid sequence set forth in SEQ ID NO: 3 in the Sequence Listing Amino acid residues corresponding to the 47th serine and 76th asparagine in the amino acid sequence described
- a sixth invention of the present invention is a method for amplifying a nucleic acid, comprising the following steps (a) to (b): (A) a step of preparing a composition containing a nucleic acid molecule as a template with the composition of the fifth invention of the present invention; and (b) reacting the composition obtained in step (a) under appropriate conditions. And a step of performing nucleic acid amplification.
- a seventh invention of the present invention is a method for suppressing the amplification of a nucleic acid having a specific base sequence in a nucleic acid amplification reaction, comprising the step of performing the nucleic acid amplification reaction in the presence of the following (a) to (d): Including: (A) an oligodeoxyribonucleotide designed to produce one or several mismatches when hybridized with a nucleic acid having the specific base sequence or a complementary strand thereof; (B) DNA polymerase; (C) at least a pair of oligonucleotide primers; and (d) the polypeptide used in the first invention of the present invention and / or the polypeptide of the fourth invention.
- the mismatch endonuclease used is another heat-resistant protein having a mismatch endonuclease activity equivalent to the polypeptide used in the first invention of the present invention or the polypeptide of the fourth invention. It may be replaced with one derived from a genus fungus.
- An eighth invention of the present invention is a method for preferentially amplifying a target nucleic acid, wherein the amplification of a nucleic acid having a base sequence different from the target nucleic acid by one or several bases is performed according to the seventh invention of the present invention
- the present invention relates to a method characterized by being suppressed by a method.
- amplification may be carried out in the presence of Proliferating cell nuclear antigen (PCNA) derived from heat-resistant bacteria or a homologue thereof.
- PCNA Proliferating cell nuclear antigen
- the ninth invention of the present invention relates to a method for detecting a mutation of a target nucleic acid using the polypeptide used in the first invention of the present invention and / or the polypeptide of the fourth invention.
- the mismatch endonuclease used is replaced with one derived from another thermostable bacterium having a mismatch endonuclease activity equivalent to the polypeptide used in the first invention of the present invention or the polypeptide of the fourth invention. May be.
- mismatch endonuclease having a different mismatch recognition sequence having high utility value in biotechnology
- a composition containing the mismatch endonuclease and a method using the mismatch endonuclease.
- 2 is a list of substrate DNAs used in the measurement of mismatch endonuclease activity of the present invention.
- 2 is a Native-PAGE result and graph showing mismatch DNA cleavage activity of the mismatch endonuclease of the present invention. It is a graph which shows the influence of pH with respect to mismatched DNA cleavage reaction of the mismatch endonuclease of this invention. It is a graph which shows the influence of sodium chloride, potassium chloride, and glutamate with respect to the mismatched DNA cleavage reaction of the mismatch endonuclease of this invention.
- mismatch refers to a base pair different from the Watson-Crick base pair present in a double-stranded nucleic acid, that is, G (guanine base) -C (cytosine base), A (adenine base) -T A base bond of a combination other than the base pair bond of (thymine base) or U (uracil base) is shown.
- polypeptide having mismatch endonuclease activity refers to a double-stranded nucleic acid.
- a nuclease having an activity of cleaving a mismatch site In addition to the activity of cleaving the phosphodiester bond adjacent to the nucleotide forming the mismatched base pair, the above-mentioned mismatched endonuclease activity can be performed at 1 to 5 base pairs, preferably 1 to 3 base pairs away from the mismatched base pair. Includes activity of cleaving adjacent phosphodiester bonds.
- the mismatch endonuclease preferably has an activity of specifically recognizing a specific mismatch base pair and cleaving a double-stranded nucleic acid. For example, at least GG, GT or TT mismatch is detected. Examples include endonucleases that recognize and cleave. The endonuclease may recognize and cleave only GG mismatch, GT mismatch, or TT mismatch only. Further, any two of the GG mismatch, GT mismatch, and TT mismatch may be recognized and cut. Furthermore, the GG mismatch, GT mismatch, and TT mismatch may all be recognized and cut.
- mismatch endonuclease is exemplified in the present invention.
- an endonuclease that recognizes and cleaves at least AA, AC, or CC mismatch can be used.
- the endonuclease may recognize and cleave only an AA mismatch, only an AC mismatch, or only a CC mismatch.
- any two of the AA mismatch, the AC mismatch, and the CC mismatch may be recognized and disconnected.
- it may be one that recognizes and cleaves all AA mismatches, AC mismatches, and CC mismatches.
- thermostable mismatch endonucleases have the activity of cleaving mismatch sites in double-stranded nucleic acids, as well as single-stranded DNA, junctions of single-stranded and double-stranded nucleic acids, double flap structures, replication forks It may have an activity of cleaving a nucleic acid by recognizing a structure, D-loop structure, and / or nicked holiday junction structure.
- the thermostable mismatch endonuclease is preferably a nuclease exhibiting an activity of cleaving a mismatch site in a double-stranded nucleic acid at a temperature of 40 ° C. or higher, preferably 50 ° C. or higher, more preferably 60 ° C. or higher. .
- thermostable mismatch endonuclease used in the present invention include a polypeptide having thermostable mismatch endonuclease activity derived from Thermococcus kodakarensis (or Thermococcus kodakaraensis). .
- the present inventors have found that a polypeptide derived from Thermococcus kodakarensis (SEQ ID NO: 1 in the sequence listing) is an endonuclease that recognizes and cleaves thermostable GG, GT, or TT mismatch. .
- a homolog of a polypeptide having the amino acid sequence shown in SEQ ID NO: 1 in the sequence listing for example, 1 to several, for example 1 to 15, preferably 1 in the amino acid sequence shown in SEQ ID NO: 1 in the sequence listing.
- a polypeptide having an amino acid sequence in which 9 to 9, more preferably 1 to 5, more preferably 1 to 3 amino acid residues are substituted, deleted, inserted and / or added, and the sequence listing A polypeptide having an amino acid sequence having 95% or more amino acid sequence identity to the amino acid sequence described in No. 1 also recognizes the heat-resistant GG, GT, or TT mismatch in the present invention. It is suitable as an endonuclease that cleaves. Further, for example, the endonuclease having the base sequence described in SEQ ID NO: 2 in the sequence listing can be preferably used.
- the present inventors have found that the 47th serine residue and the 76th asparagine residue in the amino acid sequence set forth in SEQ ID NO: 1 in the Sequence Listing are other amino acid residues, preferably the 47th is alanine, It has been found that a mutant polypeptide having an amino acid sequence in which the second is substituted with alanine is a thermostable mismatch endonuclease that specifically recognizes an AA, AC or CC mismatch. Therefore, the polypeptide having the amino acid sequence set forth in SEQ ID NO: 3 in the sequence listing prepared in this way and a homologue thereof are one embodiment of the present invention.
- Examples of the homologue of the polypeptide having the amino acid sequence set forth in SEQ ID NO: 3 in the sequence listing include one or several, excluding the 47th and 76th amino acid residues in the amino acid sequence set forth in SEQ ID NO: 3 in the sequence listing.
- An amino acid sequence in which 1 to 15, preferably 1 to 9, more preferably 1 to 5, more preferably 1 to 3 amino acid residues are substituted, deleted, inserted, and / or added.
- a polypeptide having an endonuclease activity for recognizing and cleaving AA, A-C or C-C mismatch, a 47th alanine residue in the amino acid sequence set forth in SEQ ID NO: 3 in the sequence listing A polypeptide in which the group and the 76th alanine residue are substituted with other amino acid residues, and are AA, AC or CC
- a polypeptide having endonuclease activity for recognizing and cleaving a match in the amino acid sequence of the polypeptide, 1 to several, for example, 1 to 15, preferably 1 to 1, excluding the 47th and 76th amino acid residues
- a polypeptide having endonuclease activity for recognizing and cleaving an AC or CC mismatch, and an amino acid sequence of 90% or more, preferably 95% or more with respect to the amino acid sequence shown in SEQ ID NO: 3 in the sequence listing A polypeptide having an amino acid sequence having the same identity, and the amino acid set forth in SEQ ID NO: 3 in the sequence listing
- the amino acid residue corresponding to the 47th alanine residue in the sequence is an amino acid residue other than serine
- the amino acid residue corresponding to the 76th alanine residue is an amino acid residue other than asparagine
- AA a polypeptide having an endonuclease activity that recognizes and cleaves an AC or CC mismatch.
- the endonuclease having the base sequence described in SEQ ID NO: 4 in the sequence listing can be preferably used.
- These mismatch endonucleases are suitable for various uses described later, for example, methods for excluding DNA containing a specific DNA sequence and amplifying and detecting other DNA.
- the activity of the mismatch endonuclease can be measured using a double-stranded nucleic acid containing a mismatched base pair as a substrate. Specifically, after preparing a double-stranded nucleic acid containing a mismatched base pair, an excess amount of the double-stranded nucleic acid is reacted with the mismatch endonuclease with respect to the mismatch endonuclease, and the amount of cleaved nucleic acid per unit time is determined. The activity is measured by measuring.
- the cleaved double-stranded nucleic acid can be separated and quantified from nucleic acid that has not been cleaved by electrophoresis or the like.
- double-stranded nucleic acid double-labeled with a fluorescent substance and a quencher is used so that an increase in fluorescence intensity can be detected only when cleaved
- the fluorescence intensity in the reaction solution can be measured at appropriate intervals. By doing so, the activity can be easily measured. It is also possible to examine the cleavage activity for a specific mismatched base pair by changing the base of the mismatched base pair in the double-stranded nucleic acid serving as the substrate.
- the method for cleaving double-stranded nucleic acid of the present invention is performed by adding SEQ ID NO: 1 or SEQ ID NO: 3. It is performed by acting a polypeptide having the amino acid sequence described in 3, or a homologue thereof.
- the homologue of the polypeptide having the amino acid sequence shown in SEQ ID NO: 1 or SEQ ID NO: 3 in the sequence listing is not particularly limited, but the amino acid sequence described in SEQ ID NO: 1 or SEQ ID NO: 3 in the sequence listing 1 to several, for example 1 to 15, preferably 1 to 9, more preferably 1 to 5, more preferably 1 to 3 amino acid residues are substituted, deleted, inserted, and / or 90% or more, preferably 95% or more of the amino acid sequence having an added amino acid sequence and having a mismatch endonuclease activity, and the amino acid sequence described in SEQ ID NO: 1 or SEQ ID NO: 3 in the sequence listing
- a polypeptide having an amino acid sequence having sequence identity and having a mismatch endonuclease activity is exemplified.
- a homologue of a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 or SEQ ID NO: 3 exemplified in the section “(1) Thermostable mismatch endonuclease and variant thereof of the present invention” above can be mentioned.
- the method for cleaving double-stranded nucleic acid of the present invention may be carried out in the presence of Proliferating cell nuclear antigen (PCNA) derived from heat-resistant bacteria.
- PCNA Proliferating cell nuclear antigen
- PCNA derived from Pyrococcus, Thermococcus, Methanopyrus, and Methanococcus, and homologs thereof can be used. Cleavage efficiency is improved by cleaving a double-stranded nucleic acid having a mismatch in the presence of PCNA.
- the mismatch base pair in the method for cleaving a double-stranded nucleic acid of the present invention is a double-stranded nucleic acid as long as it is present inside the double-stranded nucleic acid (between two base pairs that perform normal base pairing).
- the present invention is not limited to one having a single mismatch base pair, and a plurality of mismatch base pairs may be present at intervals, or two or more consecutive mismatch base pairs may be present. May be.
- the mismatch base pair in the method for cleaving a double-stranded nucleic acid of the present invention is preferably 1 or 8 or less consecutive mismatch base pairs present in the interior of the double-stranded nucleic acid, more preferably 1 or 4 or less consecutive mismatches.
- Examples are base pairs, even more preferably two consecutive mismatch base pairs or one mismatch base pair.
- the plurality of mismatch base pairs may be the same type of mismatch base pairs, or Different types of mismatched base pairs may be used.
- Examples of the double-stranded nucleic acid having a mismatched base pair as a target of the mismatch endonuclease include nucleic acids derived from biological samples such as PCR products, genomic DNA and fragments thereof, and synthetic nucleic acids.
- the double-stranded nucleic acid having mismatched base pairs may be a nucleic acid mixture produced by melting and re-annealing a mixture derived from a plurality of biological samples or a mixture of a nucleic acid derived from a biological sample and a synthetic nucleic acid.
- a nucleic acid having a mutation and a wild-type nucleic acid are mixed, melted and re-annealed, a mismatch base pair is formed and undergoes cleavage of the mismatch endonuclease at this site.
- the size of the nucleic acid fragment after cleavage by the mismatch endonuclease thus generated the presence or absence of mutation and the position can be verified.
- the present invention provides a mutation analysis method comprising allowing a polypeptide having the amino acid sequence described in SEQ ID NO: 1 and / or SEQ ID NO: 3 in the sequence listing or a homologue thereof to act on a double-stranded nucleic acid.
- the double-stranded nucleic acid cleavage method of the present invention can also be carried out in the course of nucleic acid amplification reaction.
- a double-stranded nucleic acid having a mismatched base pair generated by incorporation of a wrong nucleotide during the amplification process is cleaved.
- amplification of a nucleic acid having a sequence different from that of the template nucleic acid before the start of the reaction is suppressed.
- nucleic acid amplification with a reduced error rate becomes possible.
- the present invention includes a step of cleaving a double-stranded nucleic acid having a mismatched base pair using a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 and / or SEQ ID NO: 3 in the sequence listing or a homologue thereof.
- An amplification method is provided.
- composition comprising a DNA polymerase, at least a pair of oligonucleotide primers, and a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 and / or SEQ ID NO: 3 in the sequence listing or a homologue thereof, and a nucleic acid molecule as a template
- a method for amplifying a nucleic acid including a step of preparing a composition containing the product and a step of performing nucleic acid amplification by reacting the obtained composition under appropriate conditions is also an embodiment of the present invention.
- the nucleic acid amplification method is not particularly limited to the present invention, but a method for amplifying DNA is exemplified.
- a method for amplifying DNA examples include polymerase chain reaction (PCR) method, MDA (Multiple displacement amplification) method, and isothermal nucleic acid amplification methods such as ICAN method and LAMP method.
- PCNA heat-resistant bacteria-derived proliferating cell nuclear antigen
- PCNA derived from Pyrococcus, Thermococcus, Methanopyrus, and Methanococcus, and homologs thereof can be used. Cleavage efficiency is improved by cleaving a double-stranded nucleic acid having a mismatch in the presence of PCNA.
- composition of the present invention comprises a DNA polymerase, at least a pair of oligonucleotide primers, and a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 and / or SEQ ID NO: 3 in the sequence listing or a homologue thereof And is used in nucleic acid amplification methods.
- the composition used in the nucleic acid amplification method of the present invention includes a DNA polymerase, at least a pair of oligonucleotide primers, and a polypeptide having the amino acid sequence set forth in SEQ ID NO: 1 and / or SEQ ID NO: 3 in the sequence listing or a homologue thereof.
- a reaction buffer a divalent metal ion, deoxyribonucleotide, an oligonucleotide probe, and an intercalating dye
- said composition may contain further the nucleic acid used as the template of nucleic acid amplification reaction.
- the reaction buffer used in the present invention include Good buffers such as Tris-HCl and HEPES-KOH, and phosphate buffers such as sodium phosphate buffer.
- a sodium phosphate buffer or Tris-HCl buffer having a pH of 6 to 11 is preferable.
- divalent metal ions examples include magnesium ions, manganese ions, zinc ions, and cobalt ions.
- Divalent metal ions can be supplied in the form of salts such as chloride, sulfate, or acetate.
- magnesium ions have a final concentration in the range of 0.5 to 50 mM
- manganese ions have a final concentration in the range of 0.5 to 15 mM.
- the final concentration means the concentration in the reaction solution used for the nucleic acid amplification reaction (hereinafter the same).
- the composition of the present invention may contain Bovine serum albumin (BSA), a surfactant, and an inorganic salt.
- BSA Bovine serum albumin
- BSA has a final concentration in the range of 0 to 0.2 mg / ml.
- Surfactants include Tween 20, Triton X-100, and NP-40. Although not particularly limited, for example, the surfactant is in the range of 0 to 0.2% in the final concentration.
- examples of inorganic salts include sodium chloride, potassium chloride, potassium glutamate, and ammonium sulfate.
- sodium chloride has a final concentration in the range of 0 to 0.3 M
- potassium chloride has a final concentration in the range of 0 to 0.2 M
- potassium glutamate has a final concentration in the range of 0 to 0.6 M
- ammonium sulfate has The final concentration ranges from 0 to 0.05M.
- PCNA derived from heat-resistant bacteria may be included.
- PCNAs derived from the genera Pyrococcus, Thermococcus, Methanopyrus, and Methanococcus are preferred.
- the concentration of the polypeptide having a mismatch endonuclease activity in the composition for nucleic acid amplification reaction described above is suitably determined at a concentration that does not inhibit the DNA amplification reaction in each reaction system or a concentration effective for cleavage of mismatched base pairs. To decide.
- primers suitable for various nucleic acid amplification methods are selected. These may be so-called chimeric primers in which a part of the DNA is replaced with RNA in addition to DNA and RNA as long as desired amplification occurs. Further, it may be a primer containing a known nucleic acid analog or a primer labeled with a fluorescent dye for the purpose of detection or the like.
- an oligodeoxyribonucleotide designed to produce one or several mismatches when hybridized with a nucleic acid having the specific base sequence (b) a DNA polymerase, (c) at least a pair of A method of suppressing amplification of a nucleic acid having a specific base sequence in a nucleic acid amplification reaction, comprising a step of performing a nucleic acid amplification reaction in the presence of a primer and (d) a polypeptide having at least one type of mismatch endonuclease activity, 1 is one embodiment of the present invention.
- a method for preferentially amplifying a target nucleic acid by suppressing amplification of a nucleic acid having a specific base sequence that differs from the base sequence of the target nucleic acid by one or several bases using this method is also included in the present invention. It is one aspect
- the oligodeoxyribonucleotide of the above (a) is not particularly limited as long as it is designed to generate one or several mismatches when hybridized with a nucleic acid having a specific base sequence, A so-called chimeric oligodeoxyribonucleotide in which a part of DNA is substituted with RNA may be used.
- the oligodeoxyribonucleotide 3 'end may be modified to suppress the elongation reaction by DNA polymerase from the oligodeoxyribonucleotide. For example, modifications such as amination are exemplified.
- the oligodeoxyribonucleotide may be protected from cleavage from deoxyribonuclease by phosphorothioation or other modifications as long as the nucleic acid to which the oligodeoxyribonucleotide binds undergoes cleavage of the polypeptide having mismatch endonuclease activity. . Further, it may be labeled with a fluorescent dye or a quenching substance for the purpose of detection.
- the chain length of the oligodeoxyribonucleotide can be appropriately determined so that the nucleic acid having the specific base sequence can be hybridized with the oligodeoxyribonucleotide under the conditions of the reaction to be performed. Further, it is desirable that the position where a mismatch occurs when hybridized with a nucleic acid having a specific base sequence is at least 3 nucleotides away from both the 5 'end and 3' end of the oligodeoxyribonucleotide.
- the mismatch endonuclease of the present invention having an activity of specifically cleaving a mismatch site can be used for the method of suppressing amplification of a nucleic acid having a specific base sequence in the nucleic acid amplification reaction of the present invention.
- a thermostable DNA polymerase is used in a method such as a PCR method including a reaction at a high temperature as a nucleic acid amplification method, it is preferable to use a thermostable mismatch endonuclease.
- thermostable GG, GT, or TT mismatch that is, (i) an arrangement.
- a polypeptide having endonuclease activity for recognizing and cleaving a T mismatch (iii) 95% or more amino acid sequence identity to the amino acid sequence set forth in SEQ ID NO: 1 in the Sequence Listing And / or a polypeptide having an endonuclease activity that recognizes and cleaves GG, GT
- polypeptide having an endonuclease activity that recognizes and cleaves AA, AC or CC mismatch (vi) a sequence Has an amino acid sequence having an amino acid sequence identity of 90% or more, preferably 95% or more with respect to the amino acid sequence shown in SEQ ID NO: 3, and recognizes AA, AC or CC mismatch It is preferable to use a polypeptide having endonuclease activity that cleaves.
- the method for suppressing amplification of a nucleic acid having a specific base sequence in a nucleic acid amplification reaction of the present invention uses a mismatch nuclease having an activity of specifically cleaving only a double-stranded nucleic acid containing a specific mismatch base pair More preferably. In this case, it is possible to limit the base sequence to suppress amplification to one type.
- the concentration of the polypeptide having mismatched endonuclease activity may be a concentration that does not inhibit the DNA amplification reaction in each reaction system as appropriate.
- the concentration effective for cleavage of mismatched base pairs may be determined by testing.
- the concentration of the oligodeoxyribonucleotide in (a) may be determined by optimizing the use concentration in consideration of the amount of template and the amplification efficiency of the target DNA. For example, it can be carried out at a concentration of 0.1 to 10 times the concentration of the primer used in the amplification reaction.
- the method for suppressing the amplification of a nucleic acid having a specific base sequence in the nucleic acid amplification reaction of the present invention can be carried out in any nucleic acid amplification method.
- the present invention is not particularly limited, but is particularly suitable for a method of amplifying DNA.
- the present invention can be carried out by PCR, MDA, and isothermal nucleic acid amplification methods such as ICAN and LAMP.
- the method of the present invention for suppressing the amplification of a nucleic acid having a specific base sequence in a nucleic acid amplification reaction can be carried out on any nucleic acid.
- examples include DNA that is present in an artificially prepared DNA mixture, an environment-derived sample or a biological sample, or a DNA mixture prepared from the sample.
- examples of biological samples include samples derived from mammals such as humans.
- examples of the DNA mixture include a fragmented genomic DNA mixture, a cDNA mixture produced by reverse transcription reaction from mRNA, a mixture of a plurality of PCR products, and the like.
- Examples of the DNA having a specific base sequence in which amplification is suppressed include rRNA-derived reverse transcription products that remain unseparated, and low-molecular DNA generated by pairing of primers.
- the method for preferentially amplifying a target nucleic acid according to the present invention may further include a step of detecting the amplified target nucleic acid.
- this aspect of the present invention may be referred to as “the detection method of the present invention”.
- the detection method of the present invention in which DNA is a detection target, even when DNA that is not the detection target (DNA having a specific base sequence) is present in a large excess relative to the detection target DNA (target DNA)
- a DNA that is not a detection target is used as a template by the oligodeoxyribonucleotide (a) and the polypeptide having mismatch endonuclease activity (d).
- amplification of the DNA is suppressed, so that the detection target DNA can be detected.
- the detection method of the present invention makes it possible to detect a nucleic acid corresponding to a gene known to have a mutation, for example, by distinguishing the wild type from the mutant type.
- a DNA containing a wild-type base sequence as a nucleic acid having a specific base sequence and carrying out the detection method of the present invention, a large excess of normal alleles (that is, DNA having a wild-type base sequence) A small number of mutant alleles in the presence of can be detected.
- the method of the present invention is useful for detecting circulating tumor DNA in the blood and detecting a small amount of fetal DNA sequence contained in the blood of the mother.
- the mutation detection method using the mismatch endonuclease of the present invention is also an embodiment of the present invention.
- the mutation include microdeletion and point mutation.
- Polymorphisms caused by point mutations are called single nucleotide polymorphisms (SNPs).
- SNPs single nucleotide polymorphisms
- DNA having a mutant base sequence among SNPs may be described as DNA having a single nucleotide polymorphism mutation.
- Some SNPs are frequently observed in tumor cells, and others are known to be correlated with therapeutic effects and carcinogenesis by drugs for cancer treatment. Examples of such SNPs include K-ras gene, B-raf gene, and epidermal growth factor receptor (EGFR) gene SNPs.
- EGFR epidermal growth factor receptor
- Somatic cell mutations in the K-ras gene are frequently observed in colorectal cancer, lung adenocarcinoma, thyroid cancer and the like.
- B-raf gene somatic mutations are frequently observed in colorectal cancer, malignant melanoma, papillary thyroid cancer, non-small cell lung cancer, lung adenocarcinoma and the like.
- somatic mutations in the EGFR gene are frequently observed in various solid tumors. It is known that cancer treatment with EGFR inhibitors such as gefitinib and erlotinib is likely to be effective when the EGFR gene in cancer tissue has a specific single nucleotide polymorphism mutation. On the other hand, when the K-ras gene in cancer tissue has a single nucleotide polymorphism mutation, it is known that there is a high possibility of showing resistance to an EGFR inhibitor.
- the mismatch endonuclease of the present invention can be used in a mutation detection method.
- the detection method of the present invention may be carried out using, for example, DNA obtained after treating a composition containing methylated DNA extracted from a biological sample as a bisulfite. According to the detection method of the present invention, a small number of methylated alleles in the presence of a large excess of unmethylated alleles, or a small number of unmethylated alleles in the presence of a large excess of methylated alleles are detected. Detection can be performed.
- bisulfite method used for detection of methylated DNA.
- the treatment converts unmethylated cytosine to uracil, but does not change methylated cytosine. Further, when this bisulfite-treated reaction solution is amplified by PCR, uracil is converted to thymine and methylated cytosine becomes cytosine.
- detecting a small number of methylated alleles in the presence of a large excess of unmethylated alleles at a particular site or detecting a small number of unmethylated alleles in the presence of a large excess of methylated alleles, Each is to verify the presence of cytosine in a large excess of thymine, or the presence of thymine in a large excess of cytosine. If amplification from DNA containing thymine or cytosine present in a large excess can be suppressed, the presence of a small number of methylated alleles or unmethylated alleles can be easily verified.
- a probe such as electrophoresis, base sequence analysis, cycling probe or TaqMan probe
- test methods can use general techniques as they are.
- HRM High Resolution Melting
- PCNA derived from thermostable bacteria can be combined.
- PCNA derived from Pyrococcus, Thermococcus, Methanopyrus, and Methanococcus can be used.
- an oligodeoxyribonucleotide designed to generate one or several mismatches when hybridized with a nucleic acid having a specific base sequence (b) a DNA polymerase, (c) at least a pair of primers
- a composition for nucleic acid amplification reaction comprising a polypeptide having at least one mismatch endonuclease activity is also an embodiment of the present invention.
- the composition may further contain at least one selected from a reaction buffer, a divalent metal ion, a deoxyribonucleotide, an oligonucleotide probe, and an intercalating dye.
- the above composition may further contain a nucleic acid that serves as a template for the nucleic acid amplification reaction.
- the composition may contain Bovine serum albumin (BSA), a surfactant, and an inorganic salt.
- BSA Bovine serum albumin
- PCNA derived from heat-resistant bacteria may be included.
- the composition of 0.8 ⁇ ASW contained in the ASW-YT medium is 16 g / L NaCl, 2.4 g / L MgCl 2 .6H 2 O, 4.8 g / L MgSO 4 .L 7H 2 O, 0.8 g / L concentration (NH 4 ) 2 SO 4 , 0.16 g / L concentration NaHCO 3 , 0.24 g / L concentration CaCl 2 .2H 2 O, 0.4 g / L concentration KCl, 0.336 g / L concentration of KH 2 PO 4 , 0.04 g / L concentration of NaBr, 0.016 g / L concentration of SrCl 2 .6H 2 O, 0.008 g / L concentration of Fe (NH 4 ) citrate It is.
- the recovered DNA was dissolved in 100 ml of TE solution (10 mM Tris-HCl (pH 8.0), 1 mM EDTA), 0.75 mg of RNase A (manufactured by Nacalai Tesque) was added, and the mixture was reacted at 37 ° C. for 60 minutes. Thereafter, DNA was recovered by ethanol precipitation from an aqueous layer obtained by sequentially subjecting the reaction solution to phenol extraction, phenol / chloroform extraction, and chloroform extraction. Finally, 7.5 mg of DNA was obtained.
- TE solution 10 mM Tris-HCl (pH 8.0), 1 mM EDTA), 0.75 mg of RNase A (manufactured by Nacalai Tesque) was added, and the mixture was reacted at 37 ° C. for 60 minutes. Thereafter, DNA was recovered by ethanol precipitation from an aqueous layer obtained by sequentially subjecting the reaction solution to phenol extraction, phenol / chloroform extraction, and chloroform extraction. Finally,
- TKO NucS Expression Plasmid A gene encoding a polypeptide having the amino acid sequence described in SEQ ID NO: 1, ie, the TKO nucS gene was cloned by the following method. First, using 100 ng of TKO genomic DNA prepared in Preparation Example 1 as a template, TK1898-F having the base sequence described in SEQ ID NO: 5 in the sequence listing and TK1898-R having the base sequence described in SEQ ID NO: 6 in the sequence listing are used as primers PCR was performed. TK1898-F has a restriction enzyme NdeI recognition sequence, and TK1898-R has a restriction enzyme NotI recognition sequence.
- the composition of the reaction solution is a reaction volume of 50 ⁇ L using each primer concentration of 0.5 ⁇ M, 2.5 mM dNTP, 1.5 mM MgCl 2 , 1 U of KOD-Plus-Neo DNA polymerase (Toyobo Co., Ltd.).
- PCR conditions were a 30-cycle reaction with 98 ° C for 10 seconds, 55 ° C for 30 seconds, and 68 ° C for 1 minute as one cycle.
- the reaction solution was subjected to agarose electrophoresis, an approximately 800 bp band corresponding to the TKO nucS gene was excised, and DNA was purified therefrom by a conventional method.
- This DNA was digested with restriction enzymes NdeI and NotI (both manufactured by Takara Bio Inc.), and agarose electrophoresis and DNA fragment purification from gel were performed again.
- This DNA fragment was mixed with pET21a (manufactured by Novagen) previously digested with NdeI and NotI, and after ligation reaction, the transformant prepared by introducing into JM109 E. coli was cultured on ampicillin-containing LB agar medium.
- TKO nucS gene-containing plasmid was named pET21a-TkoNucS.
- TKO NucS As the expression plasmid for TKO NucS, pET21a-TkoNucS prepared in Example 1 (1) was used.
- the E. coli recombinant protein expression system (pET system) of Novagen was used.
- Escherichia coli BL21-CodonPlus (DE3) -RIL strain (manufactured by Agilent Technologies) was transformed with pET21a-TkoNucS by the method described in the instructions.
- the transformed cells were cultured until saturated with 100 ml of LB medium containing ampicillin at a concentration of 50 ⁇ g / mL and chloramphenicol at a concentration of 34 ⁇ g / mL.
- the thus obtained culture solution, OD 600 in LB medium 1L containing chloramphenicol ampicillin and 34 [mu] g / mL concentration of 50 [mu] g / mL concentration was inoculated so that 0.01, OD 600 is 0.4
- the production of the target protein was induced by adding IPTG (final concentration 1 mM).
- IPTG final concentration 1 mM
- the culture solution obtained by shaking culture at 25 ° C. for 16 hours was centrifuged (5,000 ⁇ g for 10 minutes, 4 ° C.) to recover the cells.
- the collected cells are suspended in 25 ml of a solution A (50 mM Tris-HCl (pH 8.0), 0.5 mM DTT, 0.1 mM EDTA, 10% glycerol) containing 0.5 M sodium chloride, 1 mM PMSF, and on ice.
- Ultrasonic crushing (10 seconds on / 10 seconds off for a total of 10 minutes) was performed.
- the supernatant obtained by centrifuging this ultrasonic disruption solution (24,000 ⁇ g, 10 minutes, 4 ° C.) is subjected to heat treatment (80 ° C., 30 minutes), and then centrifuged (24,000 ⁇ g, 10 minutes). 4 ° C), the heat-denatured E. coli-derived protein was removed.
- the supernatant obtained by centrifuging the dialyzed solution (23,708 ⁇ g, 10 minutes, 4 ° C.) was applied to an affinity chromatography column HisTrap Heparin HP 1 ml (manufactured by GE Healthcare). Protein was eluted with a 0.3M to 1M sodium chloride gradient and the elution fractions corresponding to 0.58-0.8M sodium chloride were collected. This fraction was dialyzed overnight against Solution A containing 0.35 M sodium chloride.
- Example 2 Enzymatic Properties of TKO NucS (1) Preparation of Substrate for Mismatch DNA Cleavage Reaction An experiment was conducted on the mismatch cleaving activity of TKO NucS.
- the oligonucleotides and their base sequences used in this example are shown in SEQ ID NOs: 7 to 16 in the Sequence Listing. Sequence numbers 7 to 9 in the sequence listing are oligonucleotides having a Cy5 fluorescent label at the 5 ′ end.
- double-stranded DNA substrates double-stranded DNA containing adenine and adenine mismatch (AA dsDNA), double-stranded DNA containing adenine and cytosine mismatch (AC dsDNA), adenine and guanine Double-stranded DNA containing a mismatch (AG dsDNA), double-stranded DNA containing a guanine-thymine mismatch (GT dsDNA), double-stranded DNA containing a guanine-guanine mismatch (GG dsDNA), Double-stranded DNA containing a mismatch between thymine and cytosine (TC dsDNA), thymine and thymine Double-stranded DNA containing a matching (T-T dsDNA), double-stranded DNA containing a mismatch of cytosine and cytosine (C-C dsDNA)) was prepared.
- AA dsDNA double-stranded DNA containing aden
- Annealing solution A (20 mM Tris-HCl (pH 8.0), 6 mM (NH 4 ) 2 SO 4 , 2 mM MgCl 2 ) containing a Cy5 fluorescently labeled oligonucleotide and an unlabeled oligonucleotide in a ratio of 1 to 1.6 )
- the aforementioned mismatched oligonucleotides were annealed in 50 ⁇ l to prepare a substrate solution containing fluorescently labeled DNA at a concentration of 50 nM.
- the annealing conditions were 98 ° C for 5 minutes, 80 ° C for 30 seconds, 80 minutes to 80 ° C for 30 minutes, 60 ° C for 30 seconds, 60 ° C to 40 ° C for 30 minutes, and 25 ° C for 30 seconds. It was.
- a substrate DNA solution containing no divalent metal ions is obtained by combining the above labeled and unlabeled oligonucleotides, annealing solution B (20 mM Tris-HCl (pH 8.0), 100 mM NaCl, 6 mM (NH 4 ) under annealing conditions. ) 2 SO 4 ) Oligonucleotides were annealed in 50 ⁇ l to prepare 50 nM fluorescently labeled DNA substrate solution.
- reaction product was detected from the gel after electrophoresis using Typhoon Trio + imager (manufactured by GE Healthcare), and the band corresponding to the oligonucleotide cleaved with Image Quant TL was quantified.
- the result is shown in FIG. In FIG. 3-B, the vertical axis represents the cutting efficiency (%), and the horizontal axis represents the concentration of TKO NucS.
- FIG. 4 is a diagram showing the optimum reaction pH, where the vertical axis shows relative activity and the horizontal axis shows pH.
- FIG. 5A is a diagram showing the influence of sodium chloride concentration
- the vertical axis shows relative activity
- the horizontal axis shows salt concentration
- FIG. 5B shows the effect of potassium chloride concentration.
- FIG. 5 is a graph showing the relative activity
- the horizontal axis shows the salt concentration
- FIG. 5C shows the effect of the potassium glutamate concentration
- the vertical axis shows the relative activity
- the horizontal axis shows the salt concentration. Indicates the concentration.
- TKO NucS 2 nM and GT dsDNA 5 nM were added thereto and incubated at 55 ° C. for 5 minutes.
- the reaction solution was treated with proteinase K and then subjected to electrophoresis to measure the cleavage activity.
- the results are shown in FIG. 6 and FIG. That is, FIG.
- FIG. 6 is a graph showing the influence of magnesium chloride concentration, where the vertical axis shows relative activity, the horizontal axis of (A) shows the concentration of 0 to 200 mM, and the horizontal axis of (B) shows 0 to 20 mM. Indicates the concentration.
- FIG. 7 is a diagram showing the influence of manganese chloride, where the vertical axis shows relative activity and the horizontal axis shows manganese chloride concentration.
- TKO NucS mismatch DNA cleavage reaction Examination of the optimum temperature in TKO NucS mismatch DNA cleavage reaction was carried out as follows. That is, it contains 20 mM Tris-HCl buffer (pH 8.0), 6 mM (NH 4 ) 2 SO 4 , 100 mM NaCl, 2 mM MgCl 2 , 0.1% Triton X-100, 0.1 mg / mL BSA A reaction solution was prepared, and TKO NucS 2 nM and GT dsDNA 5 nM were added thereto and incubated at a reaction temperature of 30 ° C. to 95 ° C. for 5 minutes.
- FIG. 8 is a diagram showing the optimum temperature, where the vertical axis shows relative activity and the horizontal axis shows reaction temperature.
- Example 3 Confirmation of Mismatch Cleavage Activity of TKO NucS (1) Cleavage Activity against Various Mismatch DNAs Double-stranded DNA (all match dsDNA) containing no 45 bp mismatch produced by annealing in Example 2 (1), Cleavage activity of TKO NucS against various mismatched DNAs was examined using 8 types of double-stranded DNA substrates each containing one mismatch.
- reaction solution (20 mM Tris-HCl (pH 8.0), 100 mM NaCl, 6 mM (NH 4 ) 2 SO 4 , 2 mM MgCl 2 , 0.1% Triton X-100, 0.1 mg / mL BSA) 20 ⁇ l
- TKO NucS monomer 0, 1, 2, 5, 10, 20, 50 and 100 nM
- 5 nM substrate all match dsDNA, AA dsDNA, AC dsDNA, AG
- dsDNA, GT dsDNA, GG dsDNA, TC dsDNA, TT dsDNA, and CC dsDNA at 55 ° C.
- FIG. 9 the vertical axis represents cutting efficiency (%), and the horizontal axis represents the concentration of TKO NucS.
- the cleavage efficiency of each mismatched substrate is represented by a different marker as shown in the legend and shown graphically. From FIG. 9, it was confirmed that TKO NucS cleaves GT dsDNA, GG dsDNA, TT dsDNA, TC dsDNA, and AG dsDNA.
- TKO NucS DNA binding activity was examined. First, in order to examine substrate specificity, a binding solution (20 mM Tris-HCl (pH 8.0), 100 mM NaCl, 6 mM (NH 4 ) 2 SO 4 , 2 mM MgCl 2 , 0.1% Triton X-100, 0.1 mg Each of TKO NucS (0, 1, 2, 5, 10, and 20 nM as monomers) in 20 ⁇ l of / mL concentration of BSA, 1 mM DTT) and the nucleotide sequence set forth in SEQ ID NO: 17 in the sequence listing, A probe DNA (ssDNA (Cy5) prepared by combining a Cy5-15 binding oligonucleotide having a Cy5 fluorescent label at the 5 ′ end and each 15 binding oligonucleotide having a base sequence set forth in SEQ ID NOs: 18 to 26 in the Sequence Listing as shown in FIG.
- ssDNA sDNA
- lanes 1 to 6 and lanes 7 to 12 correspond to 0 to 20 nM of TKO NucS, respectively. From FIG. 11, it was confirmed that TKO NucS binds to GT (15 bp) dsDNA, GG (15 bp) dsDNA, and TT (15 bp) dsDNA.
- FIG. 12 is a diagram showing heat resistance, the vertical axis shows the residual activity, and the horizontal axis shows the treatment temperature. From FIG. 12, it was confirmed that TKO NucS remained about 80% mismatch cleavage activity even after treatment at 80 ° C. for 30 minutes.
- TKO PCNA KKO karensis-derived PCNA1
- FIG. 13 shows a native-PAGE photograph.
- FIG. 13 quantifies the band intensity of the substrate and the cleavage product with Image Quant TL, the vertical axis shows relative activity, and various concentrations when the activity without PCNA is 1. Relative activity after addition of PCNA. As shown in FIG. 13, it was confirmed that the mismatch cleavage activity was promoted in the presence of TKO PCNA even in the presence of 400 mM NaCl in which reaction inhibition occurred.
- Example 5 Preparation of Mutant TKO NucS (1) Preparation of Plasmid for Expression of Mutant TKO NucS
- the plasmids described in SEQ ID NOs: 27 to 30 in the Sequence Listing were used.
- a primer having a base sequence was prepared.
- a mutant TKO NucS production plasmid a mutagenesis method using PCR was used.
- the prepared plasmid was named pET21a-TkoNucS_S47A / N76A. Moreover, the expression and purification of mutant TKO NucS S47A / N76A were performed by the method described in Example 1 (2) and (3).
- Example 6 Mismatch DNA Cleaving Activity of Mutant TKO NucS S47A / N76A
- the mismatch DNA cleaving activity of mutant TKO NucS S47A / N76A was analyzed. That is, the reaction solution (20 mM Tris-HCl (pH 8.0), 100 mM NaCl, 6 mM (NH 4 ) 2 SO 4 , 2 mM MgCl 2 , 0.1% Triton X-100, 0.1 mg / mL BSA) 20 ⁇ l Among them, 5 nM substrate (AA dsDNA), wild type TKO NucS and mutant TKO NucS S47A / N76A were added as dimers at 50 nM and reacted at 55 ° C.
- lanes 1 to 3 correspond to a reaction solution not containing TKO NucS protein, wild type TKO NucS, and mutant TKO NucS S47A / N76A, respectively.
- the mutant TKO NucS S47A / N76A recognized the AA mismatch and cleaved. From this, it was possible to produce both a mismatch endonuclease that recognizes and cleaves GG, GT, or TT mismatch and a mismatch endonuclease that recognizes and cleaves at least AA mismatch.
- the present invention is useful in a wide range of fields such as genetic engineering, biology, medicine, and agriculture.
- SEQ ID NO: 1 amino acid sequence of wild type endonuclease NucS from Thermococcus kodakarensis
- SEQ ID NO: 2 nucleotide sequence of wild type endonuclease NucS from Thermococcus kodakarensis
- SEQ ID NO: 3 amino acid sequence of mutant endonuclease NucS from Thermococcus kodakarensis
- SEQ ID NO: 4 nucleotide sequence of mutant endonuclease NucS from Thermococcus kodakarensis
- SEQ ID NO: 6 TK1898-R primer
- SEQ ID NO: 7 Substrate for TKO NucS, named as Cy5-45-nondamaged.
- SEQ ID NO: 14 Substrate for TKO NucS, named as 45-mismatch25C.
- SEQ ID NO: 15 Substrate for TKO NucS, named as 45-mismatch25T.
- SEQ ID NO: 16 Substrate for TKO NucS, named as nondamaged-22C.
- SEQ ID NO: 17 Substrate for TKO NucS, named as Cy5-15binding. "5'-end is labeled with Cy5"
- SEQ ID NO: 18 Substrate for TKO NucS, named as 15binding_AT.
- SEQ ID NO: 19 Substrate for TKO NucS, named as 15binding_AA.
- SEQ ID NO: 20 Substrate for TKO NucS, named as 15binding_CA.
- SEQ ID NO: 21 Substrate for TKO NucS, named as 15binding_GA.
- SEQ ID NO: 22 Substrate for TKO NucS, named as 15binding_GT.
- SEQ ID NO: 23 Substrate for TKO NucS, named as 15binding_GG.
- SEQ ID NO: 24 Substrate for TKO NucS, named as 15binding_CT.
- SEQ ID NO: 26 Substrate for TKO NucS, named as 15binding_CC.
Abstract
Description
代表的な例としては、セロリ由来のCelI遺伝子産物を利用する方法が知られており(特許文献2)、実際に変異塩基の解析に利用されている。しかし、この酵素は耐熱性を持たず、PCR法など高温の反応過程を含む手法には直接使用できない。このため、変異塩基の検出を行う際にも、増幅、ミスマッチ形成、ミスマッチ切断、検出の4ステップが必要となる。
この核酸増幅技術の中で代表的な技術であるポリメラーゼ連鎖反応(Polymerase Chain Reaction;PCR)法は、試験管内において簡便に所望の核酸断片を増幅する技術であり、遺伝子に関する研究のみならず、生物学、医学、農業等の幅広い分野において不可欠の実験手法となっている。PCR法は、変異型遺伝子の検出や、DNAのメチル化の解析にも応用されている。
また、等温核酸増幅方法のLAMP法やICAN法などは、特別な機器を必要としないことから、より安価な核酸検出法として使用されている。
さらに近年になり行われるようになったゲノム全体の構造解析においては、特に希少な試料からの解析を行う上で、全ゲノム増幅法は重要な技術である。
(i)配列表の配列番号1記載のアミノ酸配列を有するポリペプチド;
(ii)配列表の配列番号1に記載のアミノ酸配列において1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(iii)配列表の配列番号1に記載のアミノ酸配列に対して95%以上のアミノ酸配列の同一性を有するアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド、に関する。
(a)DNAポリメラーゼ;
(b)少なくとも一対のオリゴヌクレオチドプライマー;及び
(c)下記(i)~(iii)からなる群より選択された少なくとも一種のポリペプチド:
(i)配列表の配列番号1記載のアミノ酸配列を有するポリペプチド;
(ii)配列表の配列番号1記載のアミノ酸配列において1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(iii)配列表の配列番号1に記載のアミノ酸配列に対して95%以上のアミノ酸配列の同一性を有するアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド、に関する。
(a)本発明の第2の発明の組成物と鋳型になる核酸分子を含む組成物を調製する工程;及び
(b)工程(a)により得られた組成物を適切な条件下で反応させ、核酸増幅を行う工程、に関する。
(B)前記(A)のポリペプチドのアミノ酸配列において、47番目及び76番目のアミノ酸残基を除く1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(C)配列表の配列番号3に記載のアミノ酸配列に対して90%以上のアミノ酸配列の同一性を有するアミノ酸配列において、配列表の配列番号1に記載のアミノ酸配列における47番目のセリン及び76番目のアスパラギンに対応するアミノ酸残基が他のアミノ酸残基に置換されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド、に関する。
(a)DNAポリメラーゼ;
(b)少なくとも一対のオリゴヌクレオチドプライマー;及び
(c)下記(i)~(iii)からなる群より選択された少なくとも一種のポリペプチド:
(i)配列表の配列番号3に記載のアミノ酸配列を有するポリペプチド;
(ii)前記(i)のポリペプチドのアミノ酸配列において、47番目及び76番目のアミノ酸残基を除く1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(iii)配列表の配列番号3に記載のアミノ酸配列に対して90%以上のアミノ酸配列の同一性を有するアミノ酸配列において、配列表の配列番号1に記載のアミノ酸配列における47番目のセリン及び76番目のアスパラギンに対応するアミノ酸残基が他のアミノ酸残基に置換されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド、に関する。
(a)本発明の第5の発明の組成物と鋳型になる核酸分子を含む組成物を調製する工程;及び
(b)工程(a)により得られた組成物を適切な条件下で反応させ、核酸増幅を行う工程、に関する。
(a)前記特定の塩基配列を有する核酸またはその相補鎖とハイブリダイズさせた際に1個もしくは数個のミスマッチを生じるように設計されたオリゴデオキシリボヌクレオチド;
(b)DNAポリメラーゼ;
(c)少なくとも一対のオリゴヌクレオチドプライマー;及び
(d)本発明の第1の発明で使用するポリペプチド及び/又は第4の発明のポリペプチド、に関する。
本発明の第7の発明の方法において、使用するミスマッチエンドヌクレアーゼは、本発明の第1の発明で使用するポリペプチド又は第4の発明のポリペプチドと同等のミスマッチエンドヌクレアーゼ活性を有する別の耐熱性菌由来のものと置き換えてもよい。
本発明の第8の発明の方法において、さらに耐熱性菌由来のProliferating cell nuclear antigen (PCNA)あるいはそのホモログの存在下で増幅してもよい。
本明細書において、「ミスマッチエンドヌクレアーゼ活性を有するポリペプチド(ミスマッチエンドヌクレアーゼと記載することがある)」とは、二本鎖核酸中のミスマッチ部位を切断する活性を有するヌクレアーゼのことをいう。前記のミスマッチエンドヌクレアーゼ活性は、ミスマッチ塩基対を形成するヌクレオチドに隣接するリン酸ジエステル結合を切断する活性の他、ミスマッチ塩基対から1~5塩基対、好ましくは1~3塩基対離れたヌクレオチドに隣接するリン酸ジエステル結合を切断する活性を包含する。本発明においてミスマッチエンドヌクレアーゼは、特定のミスマッチ塩基対を特異的に認識して二本鎖核酸を切断する活性を有するものが好ましく、例えば、少なくともG-G、G-TあるいはT-Tミスマッチを認識して切断するエンドヌクレアーゼが挙げられる。前記エンドヌクレアーゼは、G-Gミスマッチのみ、G-Tミスマッチのみ、あるいはT-Tミスマッチのみを認識・切断するものであってもよい。またG-Gミスマッチ、G-Tミスマッチ及びT-Tミスマッチのうちいずれか2つのミスマッチを認識・切断するものであってもよい。さらにG-Gミスマッチ、G-Tミスマッチ及びT-Tミスマッチのすべてを認識・切断するものであってもよい。
本発明の二本鎖核酸の切断方法は、ミスマッチ塩基対を有する二本鎖核酸に配列表の配列番号1又は配列番号3に記載のアミノ酸配列を有するポリペプチド、又はそのホモログを作用させることで行われる。配列表の配列番号1又は配列番号3に記載のアミノ酸配列を有するポリペプチドのホモログとしては、本発明を特に限定するものではないが、配列表の配列番号1又は配列番号3に記載のアミノ酸配列において1ないしは数個、例えば、1ないし15個、好ましくは1ないし9個、さらに好ましくは1ないし5個、さらに好ましくは1ないし3個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつミスマッチエンドヌクレアーゼ活性を有するポリペプチド、及び配列表の配列番号1又は配列番号3に記載のアミノ酸配列に対して90%以上、好ましくは95%以上のアミノ酸配列の同一性を有するアミノ酸配列を有し、かつミスマッチエンドヌクレアーゼ活性を有するポリペプチドが例示される。例えば、上記「(1)本発明の耐熱性ミスマッチエンドヌクレアーゼ及びその変異体」のセクションで例示された配列番号1又は配列番号3に記載のアミノ酸配列を有するポリペプチドのホモログが挙げられる。
本発明のミスマッチエンドヌクレアーゼを利用することにより、PCR法などの核酸増幅法の反応液にこのミスマッチエンドヌクレアーゼを添加するだけの一段階の反応で変異解析を行うことが可能である。PCR法においては、そのサイクル数がある閾値を超えると、反応産物が増加しなくなることが知られている。添加されているdNTPの枯渇や、プライマーと反応産物のアニーリングの競合がその主な原因であるが、この時には反応産物同士のアニーリングが起こっており、変異を有する鋳型と野生型の鋳型が混在していれば、これらから増幅した反応産物同士のアニーリングにより変異部位にミスマッチ塩基対が生じることになる。したがって、本発明のミスマッチエンドヌクレアーゼの共存下でのPCRを通常よりも増加させたサイクル数で実施することだけで、変異解析が可能になる。すなわち、本発明は、配列表の配列番号1及び/又は配列番号3に記載のアミノ酸配列を有するポリペプチド又はそのホモログを二本鎖核酸に作用させることを含む、変異解析方法を提供する。
本発明の組成物は、DNAポリメラーゼ、少なくとも一対のオリゴヌクレオチドプライマー、及び配列表の配列番号1及び/又は配列番号3に記載のアミノ酸配列を有するポリペプチド又はそのホモログを含み、核酸の増幅方法に用いられる。本発明の核酸の増幅方法で用いる組成物は、DNAポリメラーゼ、少なくとも一対のオリゴヌクレオチドプライマー、及び配列表の配列番号1及び/又は配列番号3に記載のアミノ酸配列を有するポリペプチド又はそのホモログ以外に、さらに反応緩衝剤、2価の金属イオン、デオキシリボヌクレオチド、オリゴヌクレオチドプローブ、及びインターカレーティング色素から選択される少なくとも1種を含んでもよい。また、上記の組成物を核酸増幅反応に使用する場合、上記の組成物は、さらに核酸増幅反応の鋳型となる核酸を含んでいても良い。本発明に使用される反応緩衝剤としては、例えばTris-HCl、HEPES-KOH等のグッドバッファーやリン酸ナトリウムバッファー等のリン酸バッファーが挙げられる。特に限定はないが、pH6~11のリン酸ナトリウムバッファーあるいはTris-HCl緩衝液が好ましい。また、2価の金属イオンとしては、例えばマグネシウムイオン、マンガンイオン、亜鉛イオン、及びコバルトイオンが挙げられる。2価の金属イオンは、塩化物、硫酸塩、又は酢酸塩等の塩の形態で供給され得る。特に限定はされないが例えばマグネシウムイオンは終濃度で0.5~50mMの範囲、マンガンイオンは終濃度で0.5~15mMの範囲である。ここで、終濃度とは、核酸増幅反応に供する反応液中の濃度を意味する(以下、同じ)。また、本発明の組成物においては、Bovine serum albumin (BSA)、界面活性剤、無機塩を含んでいてもよい。特に限定はされないが例えばBSAは終濃度で0~0.2mg/mlの範囲である。界面活性剤としては、Tween20、TritonX-100、及びNP-40が挙げられる。特に限定はされないが例えば界面活性剤は終濃度で0~0.2%の範囲である。無機塩としては、例えば塩化ナトリウム、塩化カリウム、グルタミン酸カリウム、及び硫酸アンモニウムが挙げられる。特に限定はされないが例えば塩化ナトリウムは終濃度で0~0.3Mの範囲、塩化カリウムは終濃度で0~0.2Mの範囲、グルタミン酸カリウムは終濃度で0~0.6Mの範囲、硫酸アンモニウムは終濃度で0~0.05Mの範囲である。さらに、耐熱性菌由来のPCNAを含んでいてもよい。特に限定はされないが、Pyrococcus属、Thermococcus属、Methanopyrus属、並びにMethanococcus属由来のPCNAが好適である。
さらに、本発明者らは、本発明の基質特異性の異なるミスマッチエンドヌクレアーゼと適切に設計されたオリゴデオキシリボヌクレオチドとを利用して、核酸増幅反応において特定の塩基配列を有する核酸の増幅を抑制可能であることを見出した。従って、(a)前記特定の塩基配列を有する核酸とハイブリダイズさせた際に1個もしくは数個のミスマッチを生じるように設計されたオリゴデオキシリボヌクレオチド、(b)DNAポリメラーゼ、(c)少なくとも一対のプライマー、及び(d)少なくとも一種類のミスマッチエンドヌクレアーゼ活性を有するポリペプチドの存在下で核酸増幅反応を行う工程を含む、核酸増幅反応において特定の塩基配列を有する核酸の増幅を抑制する方法も、本発明の一態様である。また、この方法を使用して標的核酸の塩基配列と1個もしくは数個の塩基が異なる特定の塩基配列を有する核酸の増幅を抑制することによって、標的核酸を優先的に増幅する方法も本発明の一態様である。
Thermococcus kodakarensis KOD1株(JCM 12380T、以下TKOと称す)は、京都大学工学研究科の跡見晴幸教授より分与された。本株を以下の方法で培養した。即ち、ピルビン酸ナトリウム(ナカライテスク社製)5gを加えたartificial seawater(以下、ASWと称す)-YT培地(0.8×ASW、5g/L濃度のBacto Yeast Extract(DIFCO社製)、5g/L濃度のBacto Trypton(ベクトンディッキンソン社製)、0.1% resazurin(ナカライテスク社製))1Lに培地が無色になるまで硫化ナトリウムを添加した。その後、前記KOD1株を植菌し、85℃で16時間嫌気培養した後、集菌し以降の実験に用いた。なお、ASW-YT培地中に含まれる0.8×ASWの組成は、16g/L濃度のNaCl、2.4g/L濃度のMgCl2・6H2O、4.8g/L濃度のMgSO4・7H2O、0.8g/L濃度の(NH4)2SO4、0.16g/L濃度のNaHCO3、0.24g/L濃度のCaCl2・2H2O、0.4g/L濃度のKCl、0.336g/L濃度のKH2PO4、0.04g/L濃度のNaBr、0.016g/L濃度のSrCl2・6H2O、0.008g/L濃度のFe(NH4)citrateである。前記の培養で得た約2gの菌体を緩衝液L(10mM トリス-塩酸(pH8.0)、1mM EDTA、100mM NaCl)100mlに懸濁し、10%SDSを1ml加えた。この菌体懸濁液を撹拌した後、20mg/mL濃度のプロテイナーゼK(タカラバイオ社製)を1ml加えて、55℃で60分静置した。プロテイナーゼK処理後の菌体懸濁液に順次フェノール抽出、フェノール/クロロホルム抽出、クロロホルム抽出を施した後、得られた水層にエタノールを加えてDNAを沈殿させた。
回収したDNAを100mlのTE液(10mM Tris-HCl(pH8.0)、1mM EDTA)に溶解し、0.75mgのRNaseA(ナカライテスク社製)を加えて37℃で60分反応させた。その後反応液にフェノール抽出、フェノール/クロロホルム抽出、クロロホルム抽出を順次施して得られた水層より、エタノール沈殿によりDNAを回収した。最終的に7.5mgのDNAが得られた。
(1)TKO NucSの発現用プラスミドの作製
配列番号1記載のアミノ酸配列を有するポリペプチドをコードする遺伝子、すなわちTKO nucS遺伝子のクローニングは以下の方法で行なった。まず、調製例1で調製したTKOゲノムDNA 100ngを鋳型にして、配列表の配列番号5記載の塩基配列を有するTK1898-Fおよび配列表の配列番号6記載の塩基配列を有するTK1898-Rをプライマーに用いてPCRを行った。なお、TK1898-Fは制限酵素NdeIの認識配列を有し、TK1898-Rは制限酵素NotIの認識配列を有する。反応液組成は、各プライマー濃度は0.5μM、2.5mM dNTP、1.5mM MgCl2、1UのKOD-Plus-Neo DNAポリメラーゼ(東洋紡社製)を用いて50μLの反応容量である。PCR条件は、98℃ 10秒、55℃ 30秒、68℃ 1分を1サイクルとする30サイクル反応で行った。
TKO NucSの発現プラスミドであるpET21a-TkoNucSは、前記実施例1(1)で作製されたものを用いた。組換えタンパク質の産生には、ノバジェン社の大腸菌組換えタンパク質発現システム(pET system)を利用した。まず、pET21a-TkoNucSを用いて大腸菌BL21-CodonPlus(DE3)-RIL株(アジレント・テクノロジー社製)を説明書記載の方法で形質転換した。形質転換された菌体は、50μg/mL濃度のアンピシリン及び34μg/mL濃度のクロラムフェニコールを含むLB培地100mlで飽和するまで培養した。こうして得られた培養液を、50μg/mL濃度のアンピシリン及び34μg/mL濃度のクロラムフェニコールを含むLB培地1LにOD600が0.01になるように植菌し、OD600が0.4になるまで37℃で振とう培養した後、IPTGを添加する(終濃度1mM)ことで目的タンパク質の産生誘導を行った。IPTG添加後、25℃で16時間振とう培養して得た培養液を遠心分離(5,000×g 10分間、4℃)して菌体を回収した。
前記(2)で取得した熱処理、遠心分離後の上清に含まれるTKO NucSタンパク質を精製するために、まず終濃度0.15%のポリエチレンイミンをこの上清に添加して混入している核酸を不溶化した。遠心(24,000×g、10分間、4℃)により核酸を除去し、上清を得た。この上清に対して、80%飽和になるように(NH4)2SO4を加え、4℃で一晩撹拌し、目的タンパク質を塩析した。この溶液を遠心分離し(24,000×g、10分間、4℃)、得られた沈殿を1.5M (NH4)2SO4を含む溶液A20mlに溶解させ、AKTA purifierシステム(GEヘルスケア社製)を用い、疎水性相互作用カラムクロマトグラフィーカラム HiTrap Phenyl HP 5ml(GEヘルスケア社製)に供した。1.5Mから0Mの(NH4)2SO4の濃度勾配によりタンパク質を溶出し、1.4~0.73M (NH4)2SO4に相当する溶出画分を集めた。この画分を、0.3M塩化ナトリウムを含む溶液Aで一晩透析した。透析後の溶液を遠心分離(23,708×g、10分間、4℃)して得られた上清をアフィニティークロマトグラフィーカラムHisTrap Heparin HP 1ml(GEヘルスケア社製)に供した。0.3Mから1Mの塩化ナトリウムの濃度勾配によりタンパク質を溶出し、0.58~0.8M 塩化ナトリウムに相当する溶出画分を集めた。この画分を0.35M 塩化ナトリウムを含む溶液Aで一晩透析した。透析後の溶液を遠心分離(24,000×g、10分間、4℃)して得られた上清を陽イオン交換クロマトグラフィーカラムHiTrap SP HP 1ml(GEヘルスケア社製)に供した。0.35Mから1Mの塩化ナトリウムの濃度勾配によりタンパク質を溶出し、溶出画分を最終精製画分とした。この最終精製産物について12%SDS-PAGEにより純度を確認した。その結果を図1に示す。精製タンパク質の濃度はProtParam tool(http://web.expasy.org/protparam/)で得られたモル吸光係数ε280=12950M-1cm-1を用い、精製タンパク質の280nmにおける吸光度から算出した。
(1)ミスマッチDNA切断反応用基質の調製
TKO NucSのミスマッチ切断活性について実験を行った。本実施例で用いたオリゴヌクレオチドとそれらの塩基配列は配列表の配列番号7~16に示す。なお、配列表の配列番号7~9は、5’末端にCy5蛍光標識を有するオリゴヌクレオチドである。
反応溶液(20mM Tris-HCl(pH8.0)、100mM NaCl、6mM (NH4)2SO4、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSA)20μl中で各濃度のTKO NucS(単量体として0、1、2、5、10、20、50及び100nM)と5nMの基質(G-T dsDNA)を55℃、5分間反応させた後、0.5M EDTA 1μlを加え反応を停止させた。反応停止後、反応液に5mg/mL濃度のプロテイナーゼKを0.5μl加え、30分間処理することでタンパク質の分解を行った。プロテイナーゼK処理後の反応液に、ゲルローディングバッファー(15%Ficoll、10mM Tris-HCl(pH 8.0)、0.1%OrangeG) 4μlを加え、この溶液を10%ポリアクリルアミドゲルに供し、1×TBE中、25mAで30分間の電気泳動を行った。その結果を図3-Aに示す。図3-Aにおいてレーン1~8は、それぞれTKO NucSの0~100nMに相当する。さらに、電気泳動後のゲルについて、Typhoon Trio+ imager(GEヘルスケア社製)を用いて反応生成物の検出を行い、Image Quant TLで切断されたオリゴヌクレオチドに相当するバンドの定量を行った。その結果を図3-Bに示す。図3-Bにおいて縦軸は、切断効率(%)であり、横軸はTKO NucSの濃度である。
TKO NucSのミスマッチDNA切断反応における至適pHの検討は、以下のようにして行った。即ち、20mM Glycine-HCl緩衝液(pH3.0)、20mM CH3COOH-CH3COONa緩衝液(pH4.0及び、pH5.0)、20mM MES-HCl緩衝液(pH6.0)、20mM Bis-Tris-HCl緩衝液(pH7.0)、20mM Tris-HCl緩衝液(pH8.0)、20mM Glycine-NaOH緩衝液(pH9.0及びpH10.0)、20mM CAPS-NaOH緩衝液(pH11.0)、20mM Phosphate-NaOH緩衝液(pH12.0)の各緩衝液及び0.1M NaOHの溶液(pH13.0)に、40mM NaCl、10mM KCl、6mM (NH4)2SO4、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSAになるように添加したものに、さらにTKO NucS 2nMと、図2に示したG-T dsDNA (配列表の配列番号8記載の塩基配列を有するCy5-45-mismatch オリゴヌクレオチドと配列表の配列番号10記載の塩基配列を有するtemp45-normal オリゴヌクレオチドからなる2本鎖DNA)5nMを添加して55℃で5分間インキュベートした。インキュベート後、反応液をプロテイナーゼK処理し、その後電気泳動に供し切断活性を測定した。その結果を図4に示す。即ち、図4は、反応至適pHを示す図であり、縦軸は相対活性を示し、横軸はpHを示す。
塩の種類と濃度がTKO NucSのミスマッチDNA切断反応に与える影響を検討した。まず、20mM Tris-HCl緩衝液(pH8.0)、6mM (NH4)2SO4、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSAに対して、0、50、100、150、200、300、400、600、800及び1000mMのNaCl、KClあるいはK-Glu(グルタミン酸カリウム)を含む反応液を調製し、そこにTKO NucS 2nMとG-T dsDNA 5nMを添加して55℃で5分間インキュベートさせた。インキュベート後、反応液をプロテイナーゼK処理し、その後電気泳動に供し切断活性を測定した。その結果を図5に示す。即ち、図5(A)は、塩化ナトリウム濃度の影響を示す図であり、縦軸は相対活性を示し、横軸は塩濃度を示し、図5(B)は、塩化カリウム濃度の影響を示す図であり、縦軸は相対活性を示し、横軸は塩濃度を示し、図5(C)は、グルタミン酸カリウム濃度の影響を示す図であり、縦軸は相対活性を示し、横軸は塩濃度を示す。
二価金属イオンがTKO NucSのミスマッチDNA切断反応に与える影響を検討した。反応液は、20mM Tris-HCl緩衝液(pH 8.0)、6mM (NH4)2SO4、200mM NaCl、0.1%Triton X-100、0.1mg/mL濃度のBSAに対して、0、0.5、1、2、5、10、20、50、100及び200mMのMgCl2、あるいは0、0.5、1、2、5、10及び20mMのMnCl2を含む反応液を調製し、そこにTKO NucS 2nMとG-T dsDNA 5nMを添加して55℃で5分間インキュベートさせた。インキュベート後、反応液をプロテイナーゼK処理し、その後電気泳動に供し切断活性を測定した。その結果を図6、および図7に示す。即ち、図6は、塩化マグネシウム濃度の影響を示す図であり、縦軸は相対活性を示し、(A)の横軸は0~200mMの濃度を示し、(B)の横軸は0~20mM濃度を示す。同様に図7は、塩化マンガンの影響を示す図であり、縦軸は相対活性を示し、横軸は塩化マンガン濃度を示す。
TKO NucSのミスマッチDNA切断反応における至適温度の検討は以下のようにして行った。即ち、20mM Tris-HCl緩衝液(pH 8.0)、6mM (NH4)2SO4、100mM NaCl、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSAを含む反応液を調製し、そこにTKO NucS 2nMとG-T dsDNA 5nMを添加して30℃から95℃の反応温度で5分間インキュベートさせた。インキュベート後、反応液をプロテイナーゼK処理し、その後電気泳動に供し切断活性を測定した。その結果を図8に示す。即ち、図8は、至適温度を示す図であり、縦軸は相対活性を示し、横軸は反応温度を示す。
(1)様々なミスマッチDNAに対する切断活性
実施例2(1)でアニールして作製した45bpのミスマッチを含まない二本鎖DNA(all match dsDNA)と、それぞれが1か所のミスマッチを含む8種類の二本鎖DNA基質を用いて、TKO NucSの様々なミスマッチDNAに対する切断活性を検討した。即ち、反応溶液(20mM Tris-HCl(pH8.0)、100mM NaCl、6mM (NH4)2SO4、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSA)20μl中で各濃度のTKO NucS(単量体として0、1、2、5、10、20、50及び100nM)と5nMの基質(all match dsDNA、A-A dsDNA、A-C dsDNA、A-G dsDNA、G-T dsDNA、G-G dsDNA、T-C dsDNA、T-T dsDNA、及びC-C dsDNA)を55℃、5分間反応させた後、0.5M EDTA 1μlを加え反応を停止させた。反応停止後、反応液に5mg/mL濃度のプロテイナーゼKを0.5μl加え、30分間処理することでタンパク質の分解を行った。プロテイナーゼK処理後の反応液にゲルローディングバッファー 4μlを加え、この溶液を10%ポリアクリルアミドゲルに供し、1×TBE中、25mAで30分間の電気泳動を行った。電気泳動後のゲルについて、Typhoon Trio+ imager(GEヘルスケア社製)を用いて反応生成物の検出を行い、Image Quant TLで切断されたオリゴヌクレオチドに相当するバンドの定量を行った。その結果を図9に示す。図9において縦軸は、切断効率(%)であり、横軸はTKO NucSの濃度である。それぞれのミスマッチ基質の切断効率を凡例に示すような異なるマーカーで表しグラフで示した。図9から、TKO NucSは、G-T dsDNA、G-G dsDNA、T-T dsDNA、T-C dsDNA及びA-G dsDNAを切断することが確認できた。
TKO NucSのDNA結合活性について検討した。まず基質特異性を調べるため、結合溶液(20mM Tris-HCl(pH 8.0)、100mM NaCl、6mM (NH4)2SO4、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSA、1mM DTT)20μl中で各濃度のTKO NucS(単量体として0、1、2、5、10及び20nM)と配列表の配列番号17記載の塩基配列を有し、その5’末端にCy5蛍光標識を有するCy5-15bindingオリゴヌクレオチドと配列表の配列番号18~26に記載の塩基配列を有する各15bindingオリゴヌクレオチドを図10に示した組み合わせで調製したプローブDNA(ssDNA(Cy5-15binding)、all match(15bp) dsDNA、A-A(15bp)dsDNA、A-C(15bp)dsDNA、A-G(15bp)dsDNA、G-T(15bp)dsDNA、G-G(15bp)dsDNA、T-C(15bp)dsDNA、T-T(15bp)dsDNA及びC-C(15bp)dsDNA)の5nMを37℃で5分間保温した。保温終了後の反応液にゲルローディングバッファー4μlを加え、この溶液を8%ポリアクリルアミドゲルに供し、0.5×TBE中、25mAで30分間の電気泳動を行った。電気泳動後、Typhoon Trio+ imagerを用いて結合活性の検出を行った。その結果を図11に示す。図11においてレーン1~6及びレーン7~12は、それぞれTKO NucSの0~20nMに相当する。図11から、TKO NucSは、G-T(15bp)dsDNA、G-G(15bp)dsDNA及びT-T(15bp)dsDNAに結合することが確認できた。
耐熱性の検討は、以下のようにして行った。即ち、実施例3(2)の記載に従って、単量体として2nM TKO NucSを含み、かつ基質を含まない反応液 18μlを調製した。この反応液を各温度(50、60、70、80、85、90及び95℃)で30分間処理した後に5nMの基質(G-TミスマッチdsDNA)を加え、55℃、5分間反応させた後、0.5M EDTA 1μlを加え反応を停止させた。反応停止後、反応液に5mg/mL濃度のプロテイナーゼK 0.5μlを加え、30分間処理することでタンパク質の分解を行った。プロテイナーゼK処理後の反応液にゲルローディングバッファー4μlを加え、この溶液を10%ポリアクリルアミドゲルに供し、1×TBE中、25mAで30分間の電気泳動を行った。電気泳動後のゲルについてTyphoon Trio+ imagerを用いて反応生成物の検出を行い、Image Quant TLで切断されたオリゴヌクレオチドに相当するバンドの定量を行った。その結果を図12に示す。即ち、図12は、耐熱性を示す図であり、縦軸は残存活性を示し、横軸は処理温度を示す。図12から、TKO NucSは、80℃で30分間処理しても約80%のミスマッチ切断活性が残っていることが確認できた。
T.kodakarensis由来のPCNA1(Genes to Cells、2012年、第11巻、2号、p.923-937、以下TKO PCNAと称す)によるTKO NucSのミスマッチDNA切断反応への影響を検討した。即ち、塩化ナトリウム400mMを含む切断反応溶液Cの20μl中で、二量体として2.5nMの野生型TKO NucS、5nMの基質DNA(G-T dsDNA)、及び各濃度のTKO PCNA(三量体として0、5、10、25、50、125、250、500、及び1250nM)を55℃で5分間反応させた後、0.5M EDTA 1μlを加えて反応を停止させた。反応停止後、反応液に5mg/mL濃度のプロテイナーゼK 1μl及び10%SDS 1μlを加え、50℃で1時間反応させることでタンパク質の分解を行った。
プロテイナーゼK/SDS処理後の反応液にゲルローディングバッファーを4.5μl加え、この溶液を10%ポリアクリルアミドゲルに供し、1×TBE中、25mAで20分間の電気泳動を行った。
(1)変異型TKO NucSの発現用プラスミドの作製
TKO NucSの各種部位特異的変異体発現用のプラスミドを構築するため、配列表の配列番号27~30記載の塩基配列を有するプライマーを作製した。次に、変異型TKO NucS産生用プラスミドを構築するため、PCRを利用した変異導入法を用いた。
変異型TKO NucS S47A/N76AのミスマッチDNA切断活性を解析した。即ち、反応溶液(20mM Tris-HCl(pH8.0)、100mM NaCl、6mM (NH4)2SO4、2mM MgCl2、0.1%Triton X-100、0.1mg/mL濃度のBSA)20μl中で5nMの基質(A-A dsDNA)とそれぞれ野生型TKO NucS及び変異型TKO NucS S47A/N76Aを二量体として50nM添加し、55℃、5分間反応させた。その後、0.5M EDTA 1μlを加え反応を停止させた。反応停止後、反応液に5mg/mL濃度のプロテイナーゼKを0.5μl加え、30分間処理することでタンパク質の分解を行った。プロテイナーゼK処理後の反応液にゲルローディングバッファー 4μlを加え、この溶液を10%ポリアクリルアミドゲルに供し、1×TBE中、25mAで30分間の電気泳動を行った。
SEQ ID NO: 2: nucleotide sequence of wild type endonuclease NucS from Thermococcus kodakarensis
SEQ ID NO: 3: amino acid sequence of mutant endonuclease NucS from Thermococcus kodakarensis
SEQ ID NO: 4: nucleotide sequence of mutant endonuclease NucS from Thermococcus kodakarensis
SEQ ID NO: 5: TK1898-F primer
SEQ ID NO: 6: TK1898-R primer
SEQ ID NO: 7: Substrate for TKO NucS, named as Cy5-45-nondamaged. "5'-end is labeled with Cy5"
SEQ ID NO: 8: Substrate for TKO NucS, named as Cy5-45-mismatch. "5'-end is labeled with Cy5"
SEQ ID NO: 9: Substrate for TKO NucS, named as Cy5-temp45. "5'-end is labeled with Cy5"
SEQ ID NO: 10: Substrate for TKO NucS, named as temp45-normal.
SEQ ID NO: 11: Substrate for TKO NucS, named as temp45-21A.
SEQ ID NO: 12: Substrate for TKO NucS, named as temp45-21C.
SEQ ID NO: 13: Substrate for TKO NucS, named as temp45-21G.
SEQ ID NO: 14: Substrate for TKO NucS, named as 45-mismatch25C.
SEQ ID NO: 15: Substrate for TKO NucS, named as 45-mismatch25T.
SEQ ID NO: 16: Substrate for TKO NucS, named as nondamaged-22C.
SEQ ID NO: 17: Substrate for TKO NucS, named as Cy5-15binding. "5'-end is labeled with Cy5"
SEQ ID NO: 18: Substrate for TKO NucS, named as 15binding_AT.
SEQ ID NO: 19: Substrate for TKO NucS, named as 15binding_AA.
SEQ ID NO: 20: Substrate for TKO NucS, named as 15binding_CA.
SEQ ID NO: 21: Substrate for TKO NucS, named as 15binding_GA.
SEQ ID NO: 22: Substrate for TKO NucS, named as 15binding_GT.
SEQ ID NO: 23: Substrate for TKO NucS, named as 15binding_GG.
SEQ ID NO: 24: Substrate for TKO NucS, named as 15binding_CT.
SEQ ID NO: 25: Substrate for TKO NucS, named as 15binding_TT.
SEQ ID NO: 26: Substrate for TKO NucS, named as 15binding_CC.
SEQ ID NO: 27: A47-F primer
SEQ ID NO: 28: A47-R primer
SEQ ID NO: 29: A76-F primer
SEQ ID NO: 30: A76-R primer
Claims (10)
- 二本鎖核酸の切断方法であって、下記(i)~(iii)からなる群より選択された少なくとも一種のポリペプチドをミスマッチ塩基対を有する二本鎖核酸に作用させ、当該二本鎖核酸の両鎖をG-G、G-TあるいはT-Tミスマッチ塩基対部位で認識して切断することを特徴とする、方法:
(i)配列表の配列番号1記載のアミノ酸配列を有するポリペプチド;
(ii)配列表の配列番号1に記載のアミノ酸配列において1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(iii)配列表の配列番号1に記載のアミノ酸配列に対して95%以上のアミノ酸配列の同一性を有するアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド。 - 下記(a)~(c)を含む組成物:
(a)DNAポリメラーゼ;
(b)少なくとも一対のオリゴヌクレオチドプライマー;及び
(c)下記(i)~(iii)からなる群より選択された少なくとも一種のポリペプチド:
(i)配列表の配列番号1記載のアミノ酸配列を有するポリペプチド;
(ii)配列表の配列番号1記載のアミノ酸配列において1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(iii)配列表の配列番号1に記載のアミノ酸配列に対して95%以上のアミノ酸配列の同一性を有するアミノ酸配列を有し、かつG-G、G-TあるいはT-Tミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド。 - 核酸の増幅方法であって、下記(a)~(b)の工程を含む方法:
(a)請求項2に記載の組成物と鋳型になる核酸分子を含む組成物を調製する工程;及び(b)工程(a)により得られた組成物を適切な条件下で反応させ、核酸増幅を行う工程。 - 下記(A)~(C)からなる群より選択されるポリペプチド:
(A)配列表の配列番号3に記載のアミノ酸配列を有するポリペプチド、
(B)前記(A)のポリペプチドのアミノ酸配列において、47番目と76番目のアミノ酸残基を除く1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(C)配列表の配列番号3に記載のアミノ酸配列に対して90%以上のアミノ酸配列の同一性を有するアミノ酸配列において、配列表の配列番号1に記載のアミノ酸配列における47番目のセリンと76番目のアスパラギンに対応するアミノ酸残基が他のアミノ酸残基に置換されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド。 - 下記(a)~(c)を含む組成物:
(a)DNAポリメラーゼ;
(b)少なくとも一対のオリゴヌクレオチドプライマー;及び
(c)下記(i)~(iii)からなる群より選択された少なくとも一種のポリペプチド:
(i)配列表の配列番号3に記載のアミノ酸配列を有するポリペプチド;
(ii)前記(i)のポリペプチドのアミノ酸配列において、47番目と76番目のアミノ酸残基を除く1ないしは数個のアミノ酸残基が置換、欠失、挿入、及び/又は付加されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド;及び
(iii)配列表の配列番号3に記載のアミノ酸配列に対して90%以上のアミノ酸配列の同一性を有するアミノ酸配列において、配列表の配列番号1に記載のアミノ酸配列における47番目のセリンと76番目のアスパラギンに対応するアミノ酸残基が他のアミノ酸残基に置換されてなるアミノ酸配列を有し、かつA-A、A-CあるいはC-Cミスマッチを認識して切断するミスマッチエンドヌクレアーゼ活性を有するポリペプチド。 - 核酸の増幅方法であって、下記(a)~(b)の工程を含む方法:
(a)請求項5に記載の組成物と鋳型になる核酸分子を含む組成物を調製する工程;及び(b)工程(a)により得られた組成物を適切な条件下で反応させ、核酸増幅を行う工程。 - 核酸増幅反応において特定の塩基配列を有する核酸の増幅を抑制する方法であって、下記の(a)~(d)の存在下で核酸増幅反応を行う工程を含む方法:
(a)前記特定の塩基配列を有する核酸またはその相補鎖とハイブリダイズさせた際に1個もしくは数個のミスマッチを生じるように設計されたオリゴデオキシリボヌクレオチド;
(b)DNAポリメラーゼ;
(c)少なくとも一対のオリゴヌクレオチドプライマー;及び
(d)請求項1記載の方法で使用するポリペプチド及び/又は請求項4記載のポリペプチド。 - 標的核酸を優先的に増幅する方法であって、当該標的核酸と1個もしくは数個の塩基が異なる塩基配列の核酸の増幅を請求項7記載の方法で抑制することを特徴とする方法。
- 請求項8記載の方法であって、さらに耐熱性菌由来のProliferating cell nuclear antigen (PCNA)あるいはそのホモログの存在下で標的核酸の増幅を実施することを特徴する方法。
- 請求項1記載の方法で使用するポリペプチド及び/又は請求項4記載のポリペプチドを用いた標的核酸の変異検出方法。
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