WO2011142310A1 - cDNAの合成方法 - Google Patents
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- WO2011142310A1 WO2011142310A1 PCT/JP2011/060643 JP2011060643W WO2011142310A1 WO 2011142310 A1 WO2011142310 A1 WO 2011142310A1 JP 2011060643 W JP2011060643 W JP 2011060643W WO 2011142310 A1 WO2011142310 A1 WO 2011142310A1
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- endodeoxyribonuclease
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- C12N15/10—Processes for the isolation, preparation or purification of DNA or RNA
- C12N15/1096—Processes for the isolation, preparation or purification of DNA or RNA cDNA Synthesis; Subtracted cDNA library construction, e.g. RT, RT-PCR
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Definitions
- the present invention relates to a method useful for cDNA synthesis and a kit useful for cDNA synthesis.
- RNA-dependent DNA polymerases that is, reverse transcriptases
- reverse transcriptases have enabled reverse transcription reactions that synthesize cDNA using RNA as a template
- the analysis of mRNA molecules has made great strides in the development of mRNA molecules using reverse transcriptase.
- Analytical methods are now indispensable experimental methods in gene research.
- a PCR method for amplifying a DNA fragment using cDNA synthesized by reverse transcription as a template is called RT-PCR method.
- the RT-PCR method is useful not only for the cloning of mRNA-derived cDNA and the preparation of a cDNA library, but also as a method for examining the expression state of specific RNA.
- DNA is mixed in the sample used for cDNA synthesis, the region or pseudogene on the DNA encoding RNA may be amplified, so only the DNA synthesized using RNA as a template It becomes difficult to get selectively.
- a method using a nucleotide analog and a compound that lowers the Tm value during the reverse transcription reaction (Patent Document 1), or DNA in the sample is deoxyribonuclease I (hereinafter referred to as “DNA”).
- DNA deoxyribonuclease I
- a reverse transcription reaction is performed after degradation with endo-deoxyribonuclease (hereinafter sometimes referred to as endo-DNase).
- the problem to be solved by the present invention is to provide a cDNA synthesis method that can easily prevent the generation of DNA-derived amplification products mixed in a sample.
- the present inventors have found that it is possible to prepare a reaction solution composition in which endo DNase does not show activity and reverse transcriptase shows activity, and further, based on this finding, synthesis of cDNA that can solve the above problems
- the present invention regarding the method and kit for cDNA synthesis was completed.
- the present invention [1] After degrading DNA in a sample containing RNA and DNA with endodeoxyribonuclease to give a treated sample, the treated sample and reverse transcriptase can be used without heat deactivation of endodeoxyribonuclease or removal of endodeoxyribonuclease.
- a method for synthesizing cDNA comprising preparing a reaction solution containing no endodeoxyribonuclease and comprising a reaction mixture, and performing a reverse transcription reaction, [2] (a) obtaining a sample containing RNA and DNA and a composition containing endodeoxyribonuclease; (b) in a step (a) under conditions sufficient for endodeoxyribonuclease to degrade DNA in the sample. A step of treating the resulting composition; and (c) a reaction solution in which endodeoxyribonuclease does not exhibit activity is prepared by adding an additive and reverse transcriptase to the composition treated in step (b).
- the method according to [1], comprising a step of performing a reverse transcription reaction with an enzyme, [3] The method according to [1], wherein the endodeoxyribonuclease is deoxyribonuclease I, [4] The method according to [1], wherein the reverse transcriptase is a Moloney murine leukemia virus-derived reverse transcriptase, [5] The method according to [2], wherein the additive is at least one selected from the group consisting of a reducing agent, a monovalent cation and a salt thereof.
- [6] The method according to [5], wherein the monovalent cation is an ammonium ion
- [7] A method for amplifying cDNA comprising a step of performing a gene amplification reaction using the cDNA synthesized by the method according to any one of [1] to [6] as a template, and [8] (A) End Addition for preparing a composition for a reverse transcription reaction in which deoxyribonuclease, (B) buffer, (C) reverse transcriptase, and (D) reverse transcriptase are active and endodeoxyribonuclease is not active
- the present invention relates to a kit for the method according to any one of [1] to [7], comprising an agent.
- the present invention it is possible to prevent the generation of DNA-derived amplification products mixed in a sample and to synthesize cDNA with excellent operability and quantitativeness.
- FIG. 1 shows the results of agarose gel electrophoresis in Example 2.
- FIG. 2 shows the results of real-time PCR in Example 8.
- DNA in a sample containing RNA and DNA is digested with endodeoxyribonuclease to give a treated sample, and then the treatment is performed without heat deactivation of endodeoxyribonuclease or removal of endodeoxyribonuclease.
- a reverse transcription reaction is carried out by preparing a reaction solution containing a sample and reverse transcriptase and in which endodeoxyribonuclease is not active.
- thermo deactivation of endo-deoxyribonuclease means that a sample containing endo-DNase is heat-treated at 60 ° C.
- endo-DNase endo-deoxyribonuclease
- the sample used in the method of the present invention may be a sample containing RNA, for example, a sample containing RNA and DNA.
- biological samples such as cells, tissues, blood, nucleic acid-containing samples obtained by treating them with known methods, samples that may contain organisms such as food, soil, and wastewater Is exemplified.
- a nucleic acid-containing sample obtained by processing a biological sample by a known method include, for example, a cell lysate, a sample obtained by fractionating it, total RNA in the sample, or a specific RNA molecule group
- a sample enriched with mRNA may be mentioned, and a sample in which DNA is mixed may be used.
- endodeoxyribonuclease refers to an enzyme that cleaves a DNA strand into an endo-type.
- Preferred examples of endo-DNase used in the present invention include double-stranded DNA-specific endo-DNase.
- non-sequence-specific endonucleases such as DNase I and Shrim DNase and sequence-specific endonucleases such as restriction enzymes are more preferred. Is exemplified.
- the treated sample obtained by degrading the DNA in the sample with endo-DNase is not particularly limited as long as the sample is maintained under conditions such that the DNA in the sample is degraded by endo-DNase. It can prepare suitably according to DNase and a sample.
- the present invention is not particularly limited, when DNase I is used as the endo DNase, the holding conditions are preferably 20 ° C. to 45 ° C. for 10 seconds to 12 hours, more preferably 25 ° C. to 44 ° C. for 30 seconds. Examples are conditions of ⁇ 1 hour, more preferably 30 ° C. to 43 ° C. for 1 minute to 30 minutes.
- the reverse transcriptase used in the present invention may be any enzyme having reverse transcription activity, that is, an activity that synthesizes DNA complementary to RNA using RNA as a template.
- reverse transcriptase derived from Moloney murine leukemia virus (derived from MMLV) Reverse transcriptase) and avian myeloblastosis virus-derived reverse transcriptase (AMV-derived reverse transcriptase) and other virus-derived reverse transcriptases, thermophilic Bacillus bacteria-derived DNA polymerases (Bca DNA polymerase, etc.), etc.
- Examples thereof include reverse transcriptases derived from eubacteria and DNA polymerases (Tth DNA polymerase, etc.) having both reverse transcription activity derived from bacteria of the genus Thermus and DNA-dependent DNA polymerase activity.
- virus-derived reverse transcriptase is preferably used, and MMLV-derived reverse transcriptase is more preferably used.
- a reverse transcriptase either a naturally-derived enzyme or a recombinant enzyme can be used in the present invention, and a reverse transcriptase in which a naturally-occurring amino acid sequence is modified within a range having reverse transcription activity can also be used in the present invention.
- reaction solution in which endo-deoxyribonuclease does not exhibit activity is “reaction solution in which endo-deoxyribonuclease does not exhibit DNA-decomposing activity”.
- reaction solution in which endo-deoxyribonuclease does not exhibit DNA-decomposing activity 40 ⁇ g / mL of calf thymus DNA in the reaction solution A reaction solution in which the absorbance at 260 nm does not substantially change even if it is held at 25 ° C. for 10 minutes in the presence of 8 U / mL DNase I (Takara Bio Inc.) with the indicated titer on the product. To tell.
- the reaction solution containing the treated sample and reverse transcriptase and in which endo DNase does not show activity is, for example, the reaction solution after the degradation of DNA in the sample by endo DNase shows that endo DNase exhibits DNA decomposing activity. It can be prepared by adding an additive, reverse transcriptase, and other components so as to obtain a composition that does not. That is, (a) obtaining a composition comprising a sample and endodeoxyribonuclease, (b) treating the composition obtained by step (a) under conditions sufficient for endodeoxyribonuclease to degrade the DNA in the sample.
- step (c) a method in which an additive and reverse transcriptase are added to the composition treated in step (b) to prepare a reaction solution in which endodeoxyribonuclease does not exhibit activity, and a reverse transcription reaction is performed.
- the composition containing the sample and endodeoxyribonuclease in the above step (a) further includes a buffer such as Tris-HCl, a divalent metal ion such as magnesium ion or manganese ion, and dithiothreitol (hereinafter referred to as “dithiothreitol”). It is preferred that a reducing agent such as DTT) is included.
- a buffer such as Tris-HCl
- a divalent metal ion such as magnesium ion or manganese ion
- dithiothreitol dithiothreitol
- a reducing agent such as DTT
- the type and concentration of the buffer, divalent metal ion, and reducing agent are within the range where endo DNase exhibits the activity of degrading DNA in the sample in the next step (b), and the reaction characteristics and stability of endo DNase. It is preferable to set so that endo DNase exhibits high activity and high stability.
- the type and concentration of the buffer may be set near the optimum pH of endo DNase by addition thereof.
- the pH of the reaction solution can be adjusted to pH 5-10. Is preferable.
- the type and concentration of the reducing agent may be set so that endo DNase exhibits high stability.
- DNase I is used as endo DNase, 1 mM or more and less than 5 mM of DTT may be included in the composition. preferable.
- the conditions sufficient for the endodeoxyribonuclease in step (b) to degrade the DNA in the sample are that the DNA-derived product in the sample is substantially confirmed in the subsequent reverse transcription reaction and the subsequent nucleic acid amplification reaction.
- the conditions are such that the DNA is decomposed so that it can no longer be decomposed, and those skilled in the art can appropriately set according to the endo DNase and sample used.
- the present invention is not particularly limited, when DNase I is used as the endo DNase, conditions of 20 seconds to 45 ° C. for 10 seconds to 12 hours are preferably exemplified, and 25 ° C. to 44 ° C. for 30 seconds to 1 hour.
- the conditions are more preferably exemplified, and the conditions at 30 ° C. to 43 ° C. for 1 minute to 30 minutes are even more suitably exemplified.
- Examples of the additive in the step (c) include at least one selected from the group consisting of a reducing agent, a monovalent cation and a salt thereof.
- the additive can be used in the present invention, for example, in the form of an aqueous solution containing the additive, preferably a buffer solution containing the additive.
- the type and concentration of the buffer used in the above buffer solution are not particularly limited as long as the reaction solution can be adjusted to a desired pH, but by adding the buffer agent, the concentration is close to the optimum pH of the reverse transcriptase used in the reverse transcription reaction. It is preferable that the pH of the reaction solution can be changed.
- the buffering agent is not particularly limited, and a good buffer such as Tris-HCl is exemplified.
- Examples of the reducing agent include thiol reducing agents such as DTT and 2-mercaptoethanol.
- Examples of the monovalent cation include ammonium ions and alkali metal ions such as potassium ions, lithium ions, and sodium ions, and salts thereof such as ammonium sulfate and potassium chloride may be used.
- the type and amount of the reducing agent, monovalent cation or salt thereof used is such that endo-DNase does not show activity in the composition to which the additive is added and the reverse transcriptase functions effectively. There is no particular limitation, and those skilled in the art can make an appropriate decision based on the disclosure of this specification.
- the components contained in the composition in which endo DNase does not show activity and reverse transcriptase functions effectively include, for example, when endo DNase is DNase I, ammonium sulfate, DTT, and chloride.
- An example is potassium.
- the concentration of ammonium sulfate in the composition is preferably 5 mM or more, more preferably 10 mM to 30 mM, and further preferably 14 mM to 28 mM.
- the DTT concentration is preferably 5 mM or more, more preferably 11 mM to 30 mM, and further preferably 12 mM to 20 mM.
- the concentration of potassium chloride is preferably 1 mM or more, more preferably 3 mM to 30 mM, and further preferably 5 mM to 20 mM.
- the final concentration in the composition preferably includes 5 mM or more ammonium sulfate, 5 mM or more DTT, and 1 mM or more potassium chloride, more preferably 10 mM to 30 mM ammonium sulfate, 11 mM to 30 mM DTT, And 3 mM to 30 mM potassium chloride, more preferably 14 mM to 28 mM ammonium sulfate, 11 mM to 30 mM DTT, and 5 mM to 20 mM potassium chloride, more preferably 14 mM to 28 mM ammonium sulfate, 12 mM to 20 mM.
- the additive is formulated to contain DTT and 5-20 mM potassium chloride.
- said additive can be used for this invention as a buffer solution for reverse transcription reaction liquid preparation mixed with components required for reverse transcription reactions, such as reverse transcriptase, a buffer agent, an oligonucleotide primer, and dNTP. .
- components required for reverse transcription reactions such as reverse transcriptase, a buffer agent, an oligonucleotide primer, and dNTP.
- the conditions for the reverse transcription reaction are not particularly limited as long as they are sufficient to synthesize a primer extension strand complementary to the template RNA.
- the conditions sufficient for synthesizing the primer extension strand complementary to the template RNA are not particularly limited, but the temperature condition is preferably 25 to 60 ° C., more preferably 30 to 50 ° C. .
- the reaction time is preferably 5 to 120 minutes, more preferably 15 to 60 minutes.
- the reaction solution may be incubated under conditions that inactivate the reverse transcriptase. Examples of conditions for inactivating reverse transcriptase include conditions at 85 ° C. for 5 seconds.
- the cDNA amplification method of the present invention includes a step of performing a gene amplification reaction using the cDNA synthesized by the cDNA synthesis method of the present invention as a template.
- gene amplification methods well known in the art such as PCR method, ICAN method, LAMP method and SDA method can be used.
- PCR when PCR is used for nucleic acid amplification, general PCR conditions can be applied, such as dissociation (denaturation) of double-stranded template DNA into single strands, annealing of primers into single-stranded template DNA, By a reaction consisting of three steps of complementary strand synthesis (extension) from a primer, or “shuttle PCR” [“PCR Method Front Line”, “Protein Nucleic Acid Enzyme”, separate volume, Vol. 41, No. 5, pages 425-428 Among the above-mentioned three-step reactions, called “page (1996)”, the primer annealing and extension steps are performed by a two-step reaction at the same temperature.
- real-time PCR capable of monitoring nucleic acid amplification using an intercalating dye, a FRET labeled probe, or the like can also be used.
- the kit of the present invention is a kit for use in the method of synthesizing the cDNA of the present invention or the method of amplifying the cDNA of the present invention.
- A Endodeoxyribonuclease
- B Buffer
- C Reverse transcriptase
- D an additive for preparing a composition for a reverse transcription reaction in which reverse transcriptase is active and endodeoxyribonuclease is not active.
- the buffer (B) may contain a divalent metal ion necessary for endo DNase reaction.
- the additive (D) may contain an oligonucleotide primer or dNTP necessary for the reverse transcription reaction by reverse transcriptase.
- reaction solutions 1 to 5 Five types of 20 ⁇ L reaction solutions (reaction solutions 1 to 5) containing 5 U DNase I (Recombinant DNase I (RNase-free), Takara Bio Inc.), 200 ng of mouse genomic DNA, and the components shown in Table 1 were prepared. . Moreover, 5 types of reaction liquid 20microliter of the composition similar to the above was prepared except not containing DNaseI.
- the reaction solution 1 is set so that each component has a concentration half that of the standard reaction solution composition of DNase I, and the reaction solution 2 has a pH near the optimum pH of reverse transcriptase and reverse transcriptase. It is set so as to include dNTP as a substrate.
- reaction solutions were incubated at 37 ° C. for 15 minutes and then incubated at 85 ° C. for 5 seconds.
- the amount of genomic DNA remaining in each reaction solution was quantified by real-time PCR using the Rsp18 gene region as a target sequence.
- SYBR Premix ExTaq Perfect Real Time, Takara Bio Inc.
- Table 2 shows the results of quantitative determination of genomic DNA by real-time PCR and the inhibition rate of genomic DNA degradation in each reaction solution composition.
- the reaction solution 1 in which the genomic DNA in the reaction solution is completely decomposed the reaction solution added with KCl or (NH 4 ) 2 SO 4 or the reaction solution 3 to 5 with an increased DTT concentration Then, the suppression effect of DNA degradation was recognized.
- the reaction solution 4 to which (NH 4 ) 2 SO 4 was added and the reaction solution 5 in which the concentration of DTT was increased a high DNA degradation inhibitory effect was observed.
- disassembly was computed from the following formula
- Inhibition rate (%) DNA amount of reaction solution containing DNase I / DNA amount of reaction solution not containing DNase I ⁇ 100
- Example 2 Search for Reaction Composition that Suppresses End DNase Activity-2
- 6 types of reaction solutions containing 5 U of DNase I (Takara Bio Inc.), 200 ng of mouse genomic DNA, and the components shown in Table 3 (reaction solution 1 6)
- 6 types of reaction liquid 20microliter of the same composition was prepared except not containing DNaseI.
- These reaction solutions were incubated at 37 ° C. for 15 minutes and then incubated at 85 ° C. for 5 seconds. Next, each reaction solution was subjected to agarose gel electrophoresis, thereby confirming the degradation of mouse genomic DNA by DNaseI.
- FIG. 1 The result of electrophoresis is shown in FIG.
- the genomic DNA band disappeared completely by the action of DNase I.
- the compositions of the reaction solutions 3 and 4 the genomic DNA band did not disappear completely even in the presence of DNase I, and a smear-like electrophoretic image could be confirmed. From this, it was confirmed that DNase I activity was suppressed in the reaction liquids 3 and 4. Moreover, since the degree of the suppression was larger in the reaction solution 4, it was confirmed that (NH 4 ) 2 SO 4 suppresses DNase I activity in a concentration-dependent manner.
- the genomic DNA band did not change at all even in the presence of DNase I, so that it was confirmed that DNase I activity was completely suppressed in these reaction solutions.
- DNase I activity can be further suppressed by adjusting the Mg concentration in addition to adding KCl, (NH 4 ) 2 SO 4 and increasing the DTT concentration.
- DNase I can be activated by adding a separately prepared additive so that the final concentration becomes the composition of reaction solution 5 or 6 after DNA degradation with DNase I with the composition of reaction solution 1. It was suggested that another enzymatic reaction would not be possible.
- Example 3 Confirmation of DNase activity Reaction solution having components described in Reaction Solution 2 of Table 2 in Example 2 in which degradation of genomic DNA by DNase I was confirmed and Table of Example 2 in which degradation of genomic DNA was not confirmed With respect to the reaction solution having the composition described in the reaction solution 5 in 3, the DNase activity of DNase I in these reaction solutions was measured.
- the amount of enzyme that increases the absorbance of OD260 of the reaction solution by 0.001 per minute using calf thymus DNA as a substrate is 1 U.
- the reaction solution having the components described in Reaction Solution 2 in Table 3 shows an activity approximately 8 times higher than the display titer of the product, whereas the reaction having the components described in Reaction Solution 5 in Table 3 is performed.
- the activity was below the detection limit even when 30 times DNase I was used in the reaction measurement in the reaction liquid having the components described in reaction liquid 2 in Table 3. From this, it was confirmed that the activity of DNase I was completely suppressed in the reaction solution having the components described in the reaction solution 5 of Table 3.
- Example 4 Reverse transcription reaction in the presence of DNase I in a reaction composition in which DNase I does not act-1
- a reverse transcription reaction with a reverse transcriptase was performed in the reaction solution having the components described in the reaction solution 5 of Table 3 in Example 2 and the reaction solution having the components described in the reaction solution 6 of Table 3 in Example 2
- the effect of DNaseI in the reaction solution on cDNA synthesis was verified by the following method.
- the above solution containing reverse transcriptase is added to the mixed solution after DNase treatment, and the final concentrations other than reverse transcriptase, DNase I, RNase inhibitor and primer are set to the components described in Reaction Solution 5 in Table 3 or Table 3 The components described in Reaction 6 were used.
- reverse transcriptase was inactivated at 85 ° C. for 5 seconds. The amount of cDNA synthesis after the reverse transcription reaction was evaluated by real-time PCR using the Rsp18 gene region as a target sequence.
- SYBR Premix ExTaq Perfect Real Time, Takara Bio Inc.
- SYBR Premix ExTaq Perfect Real Time, Takara Bio Inc.
- Primers consisting of the nucleic acid sequence were used.
- Table 4 shows the results of real-time PCR. As shown in Table 4, there was no difference in Ct values with and without DNaseI. From this result, in the reaction solution having the components described in Reaction Solution 5 in Table 3 and the reaction solution having the components described in Reaction Solution 6 in Table 3, DNase I does not affect the cDNA synthesis by reverse transcriptase. It could be confirmed.
- Example 5 Reverse transcription reaction in the presence of DNase I in a reaction composition in which DNase I does not act-2 The amount of cDNA synthesized by reverse transcriptase in the presence of DNase I in a reaction composition in which DNase I does not act was compared with the amount of cDNA synthesized by a standard reverse transcription reaction composition not containing DNase I.
- the standard reverse transcription reaction composition not containing DNase I is 1 ⁇ L of mouse liver total RNA solution diluted serially from 2 ⁇ g / ⁇ L to 20 pg / ⁇ L, 200 U PrimeScript® RTase (Takara Bio Inc.), 20 U RNase.
- a total of 10 ⁇ L of a reaction solution containing Inhibitor (Takara Bio Inc.), 50 pmol OligodT primer, and 100 pmol Random 6mers, 50 mM Tris-HCl (pH 8.3), 75 mM KCl, and 3 mM MgCl 2 was used.
- a reverse transcription reaction was performed at 37 ° C. for 15 minutes, and then the reverse transcriptase was inactivated at 85 ° C. for 5 seconds.
- the amount of cDNA synthesis after the reverse transcription reaction was evaluated by real-time PCR using the Rsp18 gene region as a target sequence.
- SYBR Premix ExTaq Perfect Real Time, Takara Bio Inc.
- Primers consisting of the nucleic acid sequence were used.
- Table 5 shows the results of real-time PCR. As shown in Table 5, the Ct values obtained by real-time RT-PCR according to the method of the present invention almost coincided with the Ct values obtained by conventional standard real-time RT-PCR. As a result, it has been clarified that the method of the present invention can efficiently perform the reverse transcription reaction while completely suppressing the degradation of the cDNA synthesis product by DNase I.
- Example 6 Reverse transcription reaction in the presence of DNase I in a reaction composition in which DNase I does not act-3
- the amount of cDNA synthesis obtained by the cDNA synthesis method of the present invention was compared with the amount of cDNA synthesis obtained by a conventional cDNA synthesis method in which DNase I was thermally inactivated after degradation of DNA in a sample by DNase I.
- 200 U PrimeScript® RTase (Takara Bio Inc.), 20 U RNase Inhibitor (Takara Bio Inc.), 50 pmol Oligo dT primer, 100 pmol Random 6mers, 100 mM Tris-HCl (pH 8.3) 10 ⁇ L of a solution containing 1 mL of KCl, 12 mM MgCl 2 , and 1 mM dNTP was mixed. That is, the above solution containing reverse transcriptase was added to the mixed solution after DNase treatment and DNase heat inactivation treatment to obtain a composition having a standard reverse transcription reaction solution composition. Next, after performing reverse transcription reaction at 37 ° C. for 15 minutes, reverse transcriptase was inactivated at 85 ° C. for 5 seconds.
- the amount of cDNA synthesis after the reverse transcription reaction was evaluated by real-time PCR using the Rsp18 gene region as a target sequence.
- SYBR Premix ExTaq Perfect Real Time, Takara Bio Inc.
- Primers consisting of the nucleic acid sequence were used.
- Table 6 shows the results of real-time PCR.
- the Ct value in the case of using as a template the cDNA obtained by the conventional cDNA synthesis method in which DNase I is thermally inactivated after the DNA degradation in the sample is the real-time RT-PCR according to the method of the present invention.
- a delay of about 2 cycles is recognized. This is considered to be caused by the degradation of RNA used as a template for cDNA synthesis upon heat inactivation of DNaseI.
- This example demonstrates the usefulness of the cDNA synthesis method of the present invention that does not require DNase I heat inactivation.
- Example 7 Decomposition of genomic DNA in the method of the present invention Decomposition of DNA in a sample by carrying out the cDNA synthesis method of the present invention was confirmed by the following method.
- the remaining amount of mouse genomic DNA after the reaction was evaluated by real-time PCR of 40 cycles using the Rsp18 gene region as a target sequence.
- SYBR Premix ExTaq Perfect Real Time, Takara Bio Inc.
- SEQ ID NO: 1 in the sequence listing was used for real-time PCR, and as a primer pair, a primer composed of the nucleic acid sequence described in SEQ ID NO: 1 in the sequence listing and SEQ ID NO: 2 described in the sequence listing Primers consisting of the nucleic acid sequence were used.
- the Ct value in the case of using the mixed solution not containing DNase I was 22.68, whereas in the case of using the mixed solution containing DNase I, no amplification product could be confirmed. From this result, it was confirmed that the cDNA synthesis method of the present invention can avoid the generation of amplification products derived from DNA mixed in the sample.
- Example 8 Efficiency of cDNA synthesis by the method of the present invention The efficiency of cDNA synthesis by the method of the present invention was compared with the efficiency of cDNA synthesis by a method in which DNase I and reverse transcriptase were allowed to act simultaneously.
- RNA As a template, genomic DNA was removed according to the standard protocol of total RNA extraction kit NucleoSpin (registered trademark) RNA II (Machalai Nagel), and the purified mouse liver total RNA solution was serially diluted from 2 ⁇ g / ⁇ L to 20 pg / ⁇ L. We used what we did.
- NucleoSpin registered trademark
- RNA II Machalai Nagel
- the cDNA synthesis method and kit of the present invention are widely useful in the field of genetic engineering.
- SEQ ID NO: 1 Primer to amplify the cDNA fragment of mouse Rsp18 gene.
- SEQ ID NO: 2 Primer to amplify the cDNA fragment of mouse Rsp18 gene.
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Abstract
Description
[1] RNA及びDNAを含む試料中のDNAをエンドデオキシリボヌクレアーゼにより分解し処理試料とした後、エンドデオキシリボヌクレアーゼの熱失活又はエンドデオキシリボヌクレアーゼの除去を行うことなく、当該処理試料及び逆転写酵素を含有し、かつエンドデオキシリボヌクレアーゼが活性を示さない反応液を調製し、逆転写反応を行うことを特徴とする、cDNAの合成方法、
[2] (a)RNA及びDNAを含む試料ならびにエンドデオキシリボヌクレアーゼを含む組成物を得る工程、(b)エンドデオキシリボヌクレアーゼが試料中のDNAを分解するのに十分な条件で、工程(a)で得られた組成物を処理する工程、及び(c)工程(b)で処理された組成物に添加剤と逆転写酵素を加えてエンドデオキシリボヌクレアーゼが活性を示さない反応液を調製し、逆転写酵素による逆転写反応を行う工程を含む、[1]に記載の方法、
[3] エンドデオキシリボヌクレアーゼがデオキシリボヌクレアーゼIである、[1]に記載の方法、
[4] 逆転写酵素がモロニーマウス白血病ウイルス由来逆転写酵素である、[1]に記載の方法、
[5] 添加剤が、還元剤、一価カチオン及びその塩からなる群より選択された少なくとも1種である、[2]に記載の方法、
[6] 一価カチオンがアンモニウムイオンである、[5]に記載の方法、
[7] cDNAの増幅方法であって、[1]~[6]いずれかに記載の方法により合成されたcDNAを鋳型として遺伝子増幅反応を行う工程を含む方法、並びに
[8] (A)エンドデオキシリボヌクレアーゼ、(B)緩衝剤、(C)逆転写酵素、及び(D)逆転写酵素が活性を示し、かつエンドデオキシリボヌクレアーゼが活性を示さない逆転写反応用の組成物を調製するための添加剤を含む、[1]~[7]いずれかに記載の方法のためのキット
に関する。
5UのDNaseI〔Recombinant DNase I(RNase-free)、タカラバイオ社〕、200ngのマウスゲノムDNA、及び表1に記載の成分を含有する20μLの反応液を5種類(反応液1~5)調製した。また、DNaseIを含まない以外は上記と同様の組成の反応液20μLを5種類調製した。なお、反応液1は、各成分がDNaseIの標準的な反応液組成の半分の濃度となるように設定しており、反応液2は逆転写酵素の至適pH近辺のpHとなりかつ逆転写酵素の基質となるdNTPを含むように設定している。これらの反応液を37℃で15分間インキュベートした後、85℃で5秒間インキュベートした。次に、Rsp18遺伝子領域を標的配列としたリアルタイムPCRにより、各反応液中に残存するゲノムDNAの量を定量した。なお、リアルタイムPCRには、SYBR Premix ExTaq(Perfect Real Time、タカラバイオ社)を用い、プライマー対としては、配列表の配列番号1に記載の核酸配列からなるプライマー及び配列表の配列番号2に記載の核酸配列からなるプライマーを用いた。
抑制率(%)=DNaseIを含む反応液のDNA量/DNaseIを含まない反応液のDNA量×100
エンドDNase活性を完全に抑制する反応組成を構築するために、5UのDNaseI(タカラバイオ社)、200ngのマウスゲノムDNA、及び表3に示す成分を含有する反応液20μLを6種類(反応液1~6)調製した。また、DNaseIを含まない以外は同様の組成の反応液20μLを6種類調製した。これらの反応液を37℃で15分間インキュベートした後、85℃で5秒間インキュベートした。次に、各反応液をアガロースゲル電気泳動に供することにより、マウスゲノムDNAのDNaseIによる分解を確認した。
DNaseIによるゲノムDNAの分解が確認された実施例2の表3の反応液2に記載の成分を有する反応液とゲノムDNAの分解が確認されなかった実施例2の表3の反応液5に記載の組成を有する反応液について、これらの反応液中でのDNaseIのDNase活性を測定した。なお、以下に示すDNaseの活性単位は、子牛胸腺DNAを基質として反応液のOD260の吸光度を1分間に0.001増加させる酵素量を1Uとしている。
実施例2の表3の反応液5に記載の成分を有する反応液及び実施例2の表3の反応液6に記載の成分を有する反応液において、逆転写酵素による逆転写反応を行った場合に反応液中のDNaseIがcDNA合成に及ぼす影響について、以下の方法で検証した。
DNaseIが作用しない反応組成におけるDNaseI存在下の逆転写酵素によるcDNA合成量を、DNaseIを含有しない標準的な逆転写反応組成によるcDNA合成量と比較した。
本発明のcDNA合成方法により得られるcDNA合成量を、試料中のDNAのDNaseIによる分解の後にDNaseIを熱失活させる従来のcDNA合成方法により得られるcDNA合成量と比較した。
本発明のcDNAの合成方法を実施することによる試料中のDNAの分解を下記の方法により確認した。
本発明の方法によるcDNA合成の効率を、DNaseIと逆転写酵素とを同時に作用させる方法によるcDNA合成の効率と比較した。
鋳型としては、total RNA抽出キット NucleoSpin(登録商標)RNA II(マッハライ・ナーゲル社)の標準プロトコルに従ってゲノムDNAが除去され、精製されたマウス肝臓全RNA溶液を2μg/μLから20pg/μLに段階希釈したものを使用した。
上記鋳型RNA溶液を1μL、実施例2の表3の反応液1に記載の成分、0.5mMのdNTP、200UのPrimeScript(登録商標) RTase(タカラバイオ社)、20UのRNase Inhibitor(タカラバイオ社)、50pmolのOligo dT primer、100pmolのRandom 6mers、及び5UのDNaseIを含む計20μLの混合液を、鋳型RNAの濃度がそれぞれ異なる計6種類について調製した。また、鋳型RNA溶液の代わりに滅菌蒸留水1μLを添加した混合液も調製した。対照として、DNaseIを含まない以外は上記と同様の組成の混合液20μLも調製した。こうして調製した各混合液について37℃、15分間の条件で逆転写反応を行った後、85℃、5秒間の条件で逆転写酵素を失活させた。
上記(1)に記載の鋳型RNA溶液を1μL、実施例2の表3の反応液2に記載の成分、及び5UのDNaseIを含有する計10μLの混合液を、鋳型RNAの濃度がそれぞれ異なる計6種類について調製した。また、鋳型RNA溶液の代わりに滅菌蒸留水1μLを添加した混合液も調製した。対照として、DNaseIを含まない以外は上記と同様の組成の混合液10μLも調製した。こうして調製した混合液を42℃で2分間インキュベートした後、200UのPrimeScript(登録商標) RTase(タカラバイオ社)、20UのRNase Inhibitor(タカラバイオ社)、50pmolのOligo dT primerと100pmolのRandom 6mersを含有する100mMのTris-HCl(pH9.2)、20mMのKCl、20mMのDTT、1mMのdNTP、28mMの(NH4)2SO4を含む溶液を10μL添加混合した。すなわち、DNase処理後の混合液に逆転写酵素を含む上記溶液を添加し、逆転写酵素、DNaseI、RNase阻害剤及びプライマー以外の終濃度を実施例2の表3の反応液5に記載のものとした(反応液最終容量20μL)。次に、37℃で15分間の条件で逆転写反応を行った後、85℃で5秒間の条件で逆転写酵素を失活させた。
上記(2)、(3)により得られたcDNAの合成量を、Rsp18遺伝子領域を標的配列としたリアルタイムPCRにより評価した。なお、リアルタイムPCRには、SYBR Premix ExTaq(Perfect Real Time、タカラバイオ社)を用い、プライマー対としては、配列表の配列番号1に記載の核酸配列からなるプライマー及び配列表の配列番号2に記載の核酸配列からなるプライマーを用いた。リアルタイムPCRの結果を表7及び図2に示す。表7及び図2中「(3)」は上記(3)により得られたcDNAの合成量をリアルタイムPCRにより評価した結果を、「(2)」は上記(2)により得られたcDNAの合成量をリアルタイムPCRにより評価した結果を示す。
SEQ ID NO:2 ; Primer to amplify the cDNA fragment of mouse Rsp18 gene.
Claims (8)
- RNA及びDNAを含む試料中のDNAをエンドデオキシリボヌクレアーゼにより分解し処理試料とした後、エンドデオキシリボヌクレアーゼの熱失活又はエンドデオキシリボヌクレアーゼの除去を行うことなく、当該処理試料及び逆転写酵素を含有し、かつエンドデオキシリボヌクレアーゼが活性を示さない反応液を調製し、逆転写反応を行うことを特徴とする、cDNAの合成方法。
- 下記工程(a)~(c):
(a)RNA及びDNAを含む試料ならびにエンドデオキシリボヌクレアーゼを含む組成物を得る工程;
(b)エンドデオキシリボヌクレアーゼが試料中のDNAを分解するのに十分な条件で、工程(a)で得られた組成物を処理する工程;及び
(c)工程(b)で処理された組成物に添加剤と逆転写酵素を加えてエンドデオキシリボヌクレアーゼが活性を示さない反応液を調製し、逆転写酵素による逆転写反応を行う工程
を含む、請求項1に記載の方法。 - エンドデオキシリボヌクレアーゼがデオキシリボヌクレアーゼIである、請求項1に記載の方法。
- 逆転写酵素がモロニーマウス白血病ウイルス由来逆転写酵素である、請求項1に記載の方法。
- 添加剤が、還元剤、一価カチオン及びその塩からなる群より選択された少なくとも1種である、請求項2に記載の方法。
- 一価カチオンがアンモニウムイオンである、請求項5に記載の方法。
- cDNAの増幅方法であって、請求項1~6のいずれか一項に記載の方法により合成されたcDNAを鋳型として遺伝子増幅反応を行う工程を含む方法。
- 下記(A)~(D):
(A)エンドデオキシリボヌクレアーゼ、
(B)緩衝剤、
(C)逆転写酵素、及び
(D)逆転写酵素が活性を示し、かつエンドデオキシリボヌクレアーゼが活性を示さない逆転写反応用の組成物を調製するための添加剤
を含む、請求項1~7のいずれか一項に記載の方法のためのキット。
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