1. A kit for rapidly detecting new coronavirus and mutant strains based on CRISPR/Cas12a technology is characterized in that: comprises LbaCas12a, specific 501-crRNA-W sequence aiming at non-mutant strain N501, specific 501-crRNA-M sequence aiming at mutant strain Y501, RT-RAA primer or RT-PCR primer aiming at new coronavirus and mutant strain characteristic sequence, and report single-stranded DNA molecule;

the specific 501-crRNA-W sequence of the N501 is shown as SEQ ID NO: 1, the specific 501-crRNA-M sequence of Y501 is shown as SEQ ID NO: 2 is shown in the specification;

the RT-RAA primer aiming at the characteristic sequences of the new coronavirus and the mutant strain is SEQ ID NO: 3-4, wherein the primer group is 501-RT-RAA-F/R;

the RT-PCR primer aiming at the characteristic sequences of the new coronavirus and the mutant strain is SEQ ID NO: 5-6, wherein the primer group is a 501-RT-PCR-F/R primer group;

the 501-RT-RAA-F/R primer group is used for amplifying a nucleic acid fragment containing complementarity with 501-crRNA-W and/or 501-crRNA-M;

the 501-RT-PCR-F/R primer group is used for amplifying a nucleic acid fragment which is complementary to 501-crRNA-W and/or 501-crRNA-M.

2. The kit for the rapid detection of new coronavirus and mutant strain based on CRISPR/Cas12a technology according to claim 1, characterized in that:

the report single-stranded DNA molecule is SEQ ID NO: 7 or SEQ ID NO: 8.

3. a method for rapidly detecting new coronavirus and mutant strains based on CRISPR/Cas12a technology is characterized in that: the method is used for non-diagnostic or therapeutic purposes and comprises the following steps:

(1) aiming at genome sequences of wild strains and mutant strains of the new coronavirus, 501-crRNA-W and 501-crRNA-M sequences specific to non-mutation N501 and mutation Y501 sites are designed, wherein the designed crRNA sequences are shown as SEQ ID NO: 1-2, constructing 501-crRNA-W and 501-crRNA-M in-vitro transcription vectors, and performing in-vitro transcription and purification, or directly synthesizing;

(2) designing RT-RAA primers aiming at the non-mutant N501 and the mutant target Y501 of the novel coronavirus in the step (1), wherein the primer sequences are shown as SEQ ID NO: 3-4, performing RT-RAA reaction on a nucleic acid sample to be detected to obtain an RT-RAA reaction product; or designing RT-PCR primers aiming at the non-mutated N501 and the mutated target Y501 of the novel coronavirus in the step (1), wherein the primer sequences are shown as SEQ ID NO: 5-6, performing RT-PCR reaction on a nucleic acid sample to be detected to obtain an RT-PCR reaction product;

(3) mixing the purified crRNA in-vitro transcription product or the synthesized 501-crRNA-W and/or 501-crRNA-M molecule of the step (1), the RT-RAA or RT-PCR reaction product of the step (2), LbaCas12a and the report single-stranded DNA molecule in a proper system in a proper ratio for reaction;

(4) the reaction product is detected by lateral flow immunochromatographic test paper or fluorescence detection to obtain a detection result.

4. The method for the rapid detection of novel coronaviruses and mutant strains based on CRISPR/Cas12a technology according to claim 3, characterized in that:

designing a report single-stranded DNA molecule in the step (3): when the DNA is used for lateral flow immunochromatographic test paper detection, the 12-base random sequence single-stranded DNA molecule 5 '-Digoxin-NNNNNNNNNNNN-Biotin-3' with Digoxin and Biotin groups at two ends is shown in SEQ ID NO: 7;

when the fluorescent probe is used for fluorescent detection, the two ends of the single-stranded DNA molecule with the 12-base random sequence and the FAM and BHQ1 groups at the two ends respectively have 5 '-FAM-NNNNNNNNNNNN-BHQ 1-3', and the single-stranded DNA molecule is shown in SEQ ID NO: 8.

5. the method for the rapid detection of new coronavirus and mutant strain based on CRISPR/Cas12a technology according to claim 3 or 4, which is characterized in that:

when the kit is used for lateral flow immunochromatographic test paper detection, the reaction system in the step (3) is a 40 mu L system, 50-250 nM LbaCas12a, 100-500 nM 501-crRNA-W and/or 501-crRNA-M, 2 nM-4 nM report single-stranded DNA molecule, 10U RNase inhibitor, 5-20 mu L RT-RAA reaction product or RT-PCR reaction product, and 1 XNEBuffer 2.1; wherein the molar ratio of LbaCas12a to 501-crRNA-W and/or 501-crRNA-M is 1: 2;

when the fluorescent probe is used for fluorescence detection, the reaction system in the step (3) is a 20-microliter system, 50-250 nM LbaCas12a, 100-500 nM 501-crRNA-W and/or 501-crRNA-M, 500-1000 nM report single-stranded DNA molecule, 10U RNase inhibitor, 2.5-10 microliter RT-RAA reaction product or RT-PCR reaction product, and 1 XNEBbuffer 2.1; wherein the molar ratio of LbaCas12a to 501-crRNA-W and/or 501-crRNA-M is 1: 2.

6. the method for rapid detection of novel coronaviruses and mutant strains based on CRISPR/Cas12a technology according to claim 5, characterized in that:

when the kit is used for lateral flow immunochromatographic test paper detection, the reaction system in the step (3) is a 40-microliter system, 50nM LbaCas12a, 100nM 501-crRNA-W and/or 501-crRNA-M, 2nM report single-stranded DNA molecule, 10U RNase inhibitor, 5 microliter RT-RAA reaction product or RT-PCR reaction product, and 1 XNEBbuffer 2.1;

for fluorescence detection, the reaction system described in step (3) is 50nM LbaCas12a, 100nM 501-crRNA-W and/or 501-crRNA-M, 500nM reporter single stranded DNA molecule, 10U RNase inhibitor, 2.5. mu.L RT-RAA reaction product or RT-PCR reaction product, 1 XNEBbuffer 2.1 in 20. mu.L system.

7. The method for the rapid detection of new coronavirus and mutant strain based on CRISPR/Cas12a technology according to claim 3 or 4, which is characterized in that:

freeze-drying the reaction system in the step (3), wherein the freeze-drying method is that the prepared reaction system without the RT-RAA reaction product or the RT-PCR reaction product is placed in a refrigerator at the temperature of-80 ℃ for freezing overnight and then is dried in vacuum at the temperature of-50 ℃ for 12 hours; when the fluorescent probe is used for fluorescence detection, the application method of the freeze-dried reaction system comprises the steps of dissolving the freeze-dried reaction system by 10-17.5 mu L of RNA-free enzyme water, adding 2.5-10 mu L of RT-RAA reaction product or RT-PCR reaction product, and then carrying out reaction; when the reagent is used for lateral flow immune test strip detection, the application method of the freeze-dried reaction system comprises the steps of dissolving the freeze-dried reaction system by using 20-35 mu L of RNA-free enzyme water, adding 5-20 mu L of RT-RAA reaction product or RT-PCR reaction product, and then carrying out reaction.

8. The method for the rapid detection of new coronavirus and mutant strain based on CRISPR/Cas12a technology according to claim 3 or 4, which is characterized in that:

the reaction condition in the step (3) is that the reaction is carried out for 20-60 minutes at 37 ℃.

9. The method for the rapid detection of new coronavirus and mutant strain based on CRISPR/Cas12a technology according to claim 3 or 4, which is characterized in that:

the detection method of the lateral flow immunochromatographic test paper in the step (4) comprises the steps of soaking a test paper sample loading area into the reaction volume in the step (3), incubating at room temperature for 5min, and reading the strength of a detection strip by naked eyes; or other lateral flow test paper is carried out according to a corresponding color development method;

and (4) detecting the fluorescence in the step (4) by using a microplate reader or any fluorescence detection device capable of performing fluorescence excitation and detection on the FAM fluorescence channel.

10. The method for rapid detection of novel coronaviruses and mutants based on CRISPR/Cas12a technology according to claim 9, characterized in that:

the fluorescence detection in step (4) employs detection conditions in which fluorescence is excited using excitation light of a wavelength of 492nm and the fluorescence intensity is detected at a wavelength of 522 nm.

Background

As the number of infected people increases, the SARS-CoV-2 mutation is also gradually increased and accumulated. The N501Y mutation is a single base mutation located on the S protein of the novel coronavirus (SARS-CoV-2) (1501A > T on the S gene). The N501Y mutation is a key mutation in the mutation of the new coronavirus, and the N501Y mutation is shown to improve the efficiency of the virus entering cells, thereby increasing the infectivity of the virus. In addition, the N501Y mutation can reduce the neutralizing capacity of serum of a new coronary rehabilitator, and brings great instability to the prevention, control and treatment of new coronary epidemic.

The current major methods for detecting mutations in the new coronavirus are still performed by Whole Genome Sequencing (WGS) or Sanger sequencing, which is slow and not suitable for all molecular diagnostic laboratories. Therefore, the development of a rapid, sensitive, convenient and low-cost detection method and kit for the new coronavirus mutation N501Y is of great significance to epidemic prevention and treatment and early discovery of new coronavirus mutation strains in the field.

Disclosure of Invention

In order to overcome the defects and shortcomings of the prior art, the primary object of the present invention is to provide a kit for rapidly detecting new coronavirus and mutant strain based on CRISPR/Cas12a technology.

Another object of the present invention is to provide a method for rapidly detecting new coronavirus and mutant strain based on CRISPR/Cas12a technology. The method is a method for detecting N501Y mutation of new coronavirus and mutant strain by utilizing an LbaCas12a/crRNA system.

The purpose of the invention is realized by the following technical scheme:

a kit for rapidly detecting new coronavirus and mutant strains based on CRISPR/Cas12a technology comprises LbaCas12a, specific 501-crRNA-W sequence aiming at non-mutant strain N501, specific 501-crRNA-M sequence aiming at mutant strain Y501, RT-RAA primer or RT-PCR primer aiming at new coronavirus and mutant strain characteristic sequence and report single-stranded DNA molecule;

in order to better realize the invention, the kit can be combined with RT-RAA, RT-RPA and other isothermal amplification technologies or reverse transcription PCR (RT-PCR) technologies to carry out reverse transcription and amplification on the novel coronavirus nucleic acid;

preferably, the kit also comprises A Buffer, NEBuffer2.1, RNase Inhibitor, freeze-dried RT-RAA reaction microspheres and MgAc.

The specific 501-crRNA-W sequence of the N501 is shown as SEQ ID NO: 1, the specific 501-crRNA-M sequence of Y501 is shown as SEQ ID NO: 2, unlike the traditional crRNA design, the sequence is a highly specific and highly sensitive sequence obtained by introducing mutation and screening.

The RT-RAA primer aiming at the characteristic sequences of the new coronavirus and the mutant strain is a 501-RT-RAA-F/R primer group (SEQ ID NO: 3-4), and the RT-RAA primer is a high-efficiency specific sequence screened by analyzing the mutation frequency of a primer candidate region and combining the molecular epidemiology characteristics of the new coronavirus and the requirements of the RT-RAA primer through a high-throughput sequence comparison of the new coronavirus;

the RT-PCR primers aiming at the characteristic sequences of the new coronavirus and the mutant strain are 501-RT-PCR-F/R primer groups (SEQ ID NO: 5-6), and the RT-PCR primers are high-efficiency specific sequences screened by analyzing the mutation frequency of a primer candidate region and combining the molecular epidemiology characteristics of the new coronavirus and the requirements of the RT-PCR primers through the high-throughput sequence comparison of the new coronavirus;

the 501-RT-RAA-F/R primer group is used for amplifying a nucleic acid fragment containing complementarity with 501-crRNA-W and/or 501-crRNA-M;

the 501-RT-PCR-F/R primer group is used for amplifying a nucleic acid fragment which is complementary to 501-crRNA-W and/or 501-crRNA-M;

the report single-stranded DNA molecule is SEQ ID NO: 7 or SEQ ID NO: 8.

a method for rapid detection of novel coronaviruses and mutants based on CRISPR/Cas12a technology for non-diagnostic or therapeutic purposes, comprising the steps of:

(1) aiming at genome sequences of wild strains and mutant strains of the new coronavirus, 501-crRNA-W and 501-crRNA-M sequences with site specificity of non-mutation N501 and mutation Y501 are designed, and different from the traditional crRNA design, the sequences are high-specificity and high-sensitivity sequences obtained by introducing mutation and screening. The designed crRNA sequence is shown as SEQ ID NO: 1-2, constructing 501-crRNA-W and 501-crRNA-M in-vitro transcription vectors, and performing in-vitro transcription and purification, or directly synthesizing;

(2) designing RT-RAA primers aiming at the non-mutation N501 and the mutation target Y501 of the new coronavirus in the step (1), wherein the RT-RAA primers are sequences with low mutation frequency (less than one thousandth) screened out by counting the mutation frequency of each base through high-throughput sequence comparison of the new coronavirus. And according to the design principle of RT-RAA primers, a sequence with good amplification efficiency and high specificity is obtained by screening and verifying the low-mutation-frequency and specific sequences and is used as the RT-RAA primers, and the primer sequence is shown as SEQ ID NO: 3-4, performing RT-RAA reaction on a nucleic acid sample to be detected to obtain an RT-RAA reaction product; or designing RT-PCR primers aiming at the non-mutated N501 and the mutated target Y501 of the new coronavirus in the step (1), wherein the RT-PCR primers are sequences with low mutation frequency (less than one ten thousandth) screened out by carrying out high-throughput sequence comparison on the new coronavirus and counting the mutation frequency of each base. And according to the design principle of RT-PCR primers, a sequence with good amplification efficiency and high specificity is obtained by screening and verifying the low-mutation-frequency and specific sequences and is used as the RT-PCR primers, and the primer sequence is shown as SEQ ID NO: 5-6, performing RT-PCR reaction on a nucleic acid sample to be detected to obtain an RT-PCR reaction product;

(3) mixing the purified crRNA in-vitro transcription product or the synthesized 501-crRNA-W and/or 501-crRNA-M molecule of the step (1), the RT-RAA or RT-PCR reaction product of the step (2), LbaCas12a and the report single-stranded DNA molecule in a proper system in a proper ratio for reaction; selecting optimal reaction time through continuous kinetic study in the reaction process;

(4) the reaction product is detected by lateral flow immunochromatographic test paper or fluorescence detection to obtain a detection result.

Preferably, in step (1), the NCBI accession number of the genome of the new coronavirus wild strain is NC _045512.2, and the NCBI accession number of the mutant reference gene sequence is MW 803161.1.

Preferably, the method for synthesizing the 501-crRNA-W and 501-crRNA-M sequences to be designed in the step (1) comprises the following steps: constructing 501-crRNA-W and 501-crRNA-M in vitro transcription vectors and performing in vitro transcription and purification, or direct chemical synthesis, but not limited thereto.

Preferably, the nucleic acid sample to be detected in step (2) may be nucleic acid extracted from a clinical sample, or a sample treated by a sample treatment method in other nucleic acid detection means.

Preferably, the LbaCas12a described in step (3) can be obtained by recombinant expression and purification or use the LbaCase12a product of NEB;

preferably, the design of the report single-stranded DNA molecule in step (3): when the DNA is used for lateral flow immunochromatographic test paper detection, the two ends of the DNA respectively carry Digoxin and Biotin groups, and the DNA has a 12-base random sequence single-stranded DNA molecule 5 '-Digoxin-NNNNNNNNNNNN-Biotin-3' (SEQ ID NO: 7), but the DNA is not limited to the molecule;

when the fluorescent probe is used for fluorescence detection, the 12-base random sequence single-strand DNA molecule 5 '-FAM-NNNNNNNNNNNN-BHQ 1-3' (SEQ ID NO: 8) with FAM and BHQ1 groups at two ends is adopted, but the fluorescent probe is not limited to the above.

Preferably, when the lateral flow immunochromatographic test strip is used for detection, the reaction system in the step (3) is a 40-microliter system, 50-250 nM LbaCas12a, 100-500 nM 501-crRNA-W and/or 501-crRNA-M, 2 nM-4 nM report single-stranded DNA molecule, 10U RNase inhibitor (TaKaRa), 5-20 microliter RT-RAA reaction product or RT-PCR reaction product, 1 XNEBuffer 2.1; wherein the molar ratio of LbaCas12a to 501-crRNA-W and/or 501-crRNA-M is 1: 2;

further preferably, when the reagent kit is used for lateral flow immunochromatographic test strip detection, the reaction system in the step (3) is a 40-L system, 50nM LbaCas12a, 100nM 501-crRNA-W and/or 501-crRNA-M, 2nM reporter single-stranded DNA molecule, 10U RNase inhibitor (TaKaRa), 5. mu.L RT-RAA reaction product or RT-PCR reaction product, 1 XNEBbuffer 2.1;

preferably, when the fluorescent probe is used for fluorescence detection, the reaction system in the step (3) is a 20-microliter system, 50-250 nM LbaCas12a, 100-500 nM 501-crRNA-W and/or 501-crRNA-M, 500-1000 nM report single-stranded DNA molecule, 10U RNase inhibitor (TaKaRa), 2.5-10 microliter RT-RAA reaction product or RT-PCR reaction product, 1 XNEBbuffer 2.1; wherein the molar ratio of LbaCas12a to 501-crRNA-W and/or 501-crRNA-M is 1: 2;

further preferably, when used for fluorescence detection, the reaction system described in step (3) is a 20. mu.L system with 50nM LbaCas12a, 100nM 501-crRNA-W and/or 501-crRNA-M, 500nM reporting single-stranded DNA molecule, 10U RNase inhibitor (TaKaRa), 2.5. mu.L RT-RAA reaction product or RT-PCR reaction product, 1 XNEBbuffer 2.1;

preferably, the reaction system in the step (3) can be lyophilized, wherein the lyophilized method is that the prepared reaction system (without RT-RAA reaction product or RT-PCR reaction product) is frozen in a refrigerator at-80 ℃ overnight and then vacuum-dried at-50 ℃ for 12 h; when the fluorescent probe is used for fluorescence detection, the application method of the freeze-dried reaction system comprises the steps of dissolving the freeze-dried reaction system by 10-17.5 mu L of RNA-free enzyme water, adding 2.5-10 mu L of RT-RAA reaction product or RT-PCR reaction product, and then carrying out reaction; when the reagent is used for lateral flow immune test strip detection, the application method of the freeze-dried reaction system comprises the steps of dissolving the freeze-dried reaction system by using 20-35 mu L of RNA-free enzyme water, adding 5-20 mu L of RT-RAA reaction product or RT-PCR reaction product, and then carrying out reaction.

Preferably, the reaction in the step (3) is carried out at 37 ℃ for 20-60 minutes; more preferably 30 minutes.

Preferably, the design of the lateral flow immunochromatographic test strip in step (4): the lateral flow immunochromatographic test strip adopts a commercial lateral flow chromatography detection test strip (Magigen), and an upper sample region, a Gold-NP anti-digoxin antibody region, a streptavidin strip (namely a detection strip) and an anti-antibody strip (namely a quality control strip) are sequentially arranged on the lateral flow immunochromatographic test strip.

Preferably, the detection method of the lateral flow immunochromatographic test strip in the step (4) is to soak the sample loading area of the test strip into the reaction volume in the step (3), incubate for 5min at room temperature, and read the strength of the detection strip by naked eyes; or other lateral flow test strips are carried out according to a corresponding color development method.

Preferably, the detection device used in the fluorescence detection in step (4) can be a conventional microplate reader or any fluorescence detection device capable of performing fluorescence excitation and detection on FAM fluorescence channels.

More preferably, the fluorescence detection in step (4) is carried out under such conditions that the fluorescence is excited by excitation light having a wavelength of 492nm and the fluorescence intensity is detected at a wavelength of 522 nm.

The mechanism of the invention is as follows:

the LbaCas12 enzyme can target DNA complementary with the LbaCas12 enzyme under the guidance of a characteristic crRNA sequence, activate cis-reaction activity of the LbaCas12 enzyme, simultaneously activate trans-cleavage activity of the LbaCas12 enzyme, and nonspecifically cleave a single-stranded DNA probe molecule marked by fluorescence or biotin, so that the LbaCas12 enzyme can be detected by fluorescence or lateral flow immunodipstick.

According to the invention, through the single base resolution capability of the LbaCas12/crRNA system, 501-crRNA-W and 501-crRNA-M aiming at a non-mutated target N501 and a mutated target Y501 of a new coronavirus are respectively designed, and when two crRNAs are used for simultaneously detecting the same sample, whether a nucleic acid sample to be detected is a mutant strain or a mutant strain can be effectively distinguished according to the difference of detection results.

Compared with the prior art, the invention has the following advantages and effects:

compared with the existing sequencing method for detecting the mutation of the new coronavirus N501Y, the method provided by the invention has the advantages that the sample molecules are detected by utilizing the LbaCas12a/crRNA, only one PCR instrument or a constant temperature device and a simple and easy fluorescence reading device are needed, the N501Y mutant strain can be rapidly distinguished from the new coronavirus positive sample, and meanwhile, the method has the characteristics of high specificity, high sensitivity and low cost, and is more widely suitable for various molecular diagnosis laboratories. The invention can quickly and effectively distinguish the new coronavirus non-mutant strain and the mutant strain, and has important significance for preventing and controlling the new coronavirus epidemic situation.

Drawings

FIG. 1 shows the specific 501-crRNA-W and 501-crRNA-M targets designed by the new coronavirus against the non-mutant strain (WT) N501 and the mutant strain (MT) Y501, and their PAM (TTTN) sequences.

FIG. 2 shows the results of fluorescence detection of N501 non-mutant strain and Y501 mutant strain of the novel coronavirus by RT-PCR-Cas12a nucleic acid detection system in example 1; wherein, the detection samples are Y501(MT) with different concentrations, and the RT-RCR amplification primers adopt the nucleotide sequences shown in SEQ ID NO: 5-6; n-3, concentration of target nucleic acid 10^-14M，10^-15M，10^-16M，10^-17M, BC (blank control), error bars: ± SD,. x: p is a radical of<0.0001。

FIG. 3 shows the results of fluorescence detection of N501 non-mutant and Y501 mutant of the novel coronavirus in RT-RAA-Cas12a nucleic acid detection system in example 1; wherein the detection sample is Y501(MT) with different concentrations, and the RT-RAA amplification primer adopts the sequence shown in SEQ ID NO: 3-4; n-3, concentration of target nucleic acid 10^-16M，10^-17M, BC (blank control), error bars: ± SD,. x: p is a radical of<0.0001。

FIG. 4 is an embodimentThe results of RT-PCR-Cas12a nucleic acid detection system lateral flow test paper method for detecting N501 non-mutant strain and Y501 mutant strain of new coronavirus in example 2; wherein, the detection sample is Y501(MT) with different concentrations, and the RT-PCR amplification primer adopts SEQ ID NO: 5-6; target nucleic acid concentration of 10^-13M， 10^-14M，10^-15M，10^-16M, BC (blank control); w and M correspond to 501-crRNA-W and 501-crRNA-M, respectively.

FIG. 5 shows the results of detection of N501 non-mutant strain and Y501 mutant strain of new coronavirus by RT-RAA-Cas12a nucleic acid detection system lateral flow test paper method in example 2; wherein the detection sample is Y501(MT) with different concentrations, and the RT-RAA amplification primer adopts the sequence shown in SEQ ID NO: 3-4; target nucleic acid concentration of 10^-13M， 10^-14M，10^-15M，10^-16M, BC (blank control); w and M correspond to 501-crRNA-W and 501-crRNA-M, respectively.

Detailed Description

The present invention will be described in further detail with reference to the following examples and drawings, but the mode of carrying out the invention is not limited thereto.

The test methods in the following examples, in which specific experimental conditions are not specified, are generally performed according to conventional experimental conditions or according to the experimental conditions recommended by the manufacturer.

Example 1:

in the embodiment of the invention, the CRISPR/Cas12a technology-based method for rapidly detecting the characteristic sequence nucleic acid of the non-mutant and mutant strains of the novel coronavirus is used for non-diagnosis or treatment purposes and comprises the following steps:

(1) the characteristic 501-crRNA-W and 501-crRNA-M are designed respectively for the non-mutated N501 (codon AAT) and the mutated Y501 (codon TAT) of the new coronavirus (SARS-CoV-2), which are different from the conventional crRNA design, and are highly specific and highly sensitive sequences obtained by introducing mutation and screening, such as SEQ ID NOs: 1-2, then constructing transcription vectors of 501-crRNA-W and 501-crRNA-M, and then transcribing and purifying.

TABLE 1crRNA sequence, RT-RAA primer, RT-PCR primer sequence

Name (R)		Sequence of
			501-crRNA-W	SEQ ID NO：1	UUUC caUcccacuaaugguguu
501-crRNA-M	SEQ ID NO：2	UUUC caUcccacuUaugguguu
			501-RT-RAA-F	SEQ ID NO：3	cctgtatagattgtttaggaagtctaatctc
501-RT-RAA-R	SEQ ID NO：4	cctgttaaaccattgaagttgaaattgacac
			501-RT-PCR-F	SEQ ID NO：5	ctcaaaccttttgagagaga
501-RT-PCR-R	SEQ ID NO：6	atgtctctgccaaattgttg

Specifically, the method for crRNA in vitro transcription comprises the following steps: the reaction was carried out for 16 hours at 37 ℃ in the following system: nuclean-free water was added to 20. mu.L each of 1.5. mu.L of NTP, 1.5. mu.L of 10 × reaction buffer, 1. mu.g of Template DNA, and 1.5. mu.L of T7 RNA Polymerase Mix.

Specifically, the purification method of the crRNA transcript comprises the following steps: after the transcription product was treated with DNaseI (TaKaRa) for 15 minutes, the transcribed crRNA was purified using NEB RNA clean Kit or other RNA purification Kit.

(2) Aiming at published new coronavirus genomes (genome sequence information is derived from new coronavirus sequences submitted by countries of GISAID (as far as 2021, 01, 13), 360482 sequences are obtained in total, https:// www.gisaid.org /), relatively conservative and specific regions are selected near a 501-crRNA-W/M target point to serve as primers of RT-RAA, the RT-RAA primers are sequences with low mutation frequency (less than one thousandth) selected by counting mutation frequency of each base through high-throughput sequence comparison of the new coronaviruses. And then according to the design principle of RT-RAA primers, sequences with good amplification efficiency and high specificity are obtained by screening and verifying from the low mutation frequency and specific sequences and are used as RT-RAA primers, and SEQ ID NO: 3 to 4.

The pretreatment method of the nucleic acid sample to be detected is to carry out RT-RAA amplification on 2 mu L of sample solution, and the obtained amplification product is the processed nucleic acid sample; the nucleic acid sample to be tested is in this example an in vitro transcribed RNA molecule comprising the designed targeting segment.

RT-RAA reaction system: in a 50. mu.L system, 400nM of the upstream primer (501-RT-RAA-F), 400nM of the downstream primer (501-RT-RAA-R), 41.5. mu.L of A Buffer (purchased from Mass-testing Bio Inc.) and 2. mu.L of the nucleic acid sample template to be tested were used. The above systems were mixed and added to lyophilized RT-RAA reaction microspheres, magnesium acetate MgAc 280mM 2.5. mu.L was added and the reaction was started at 37 ℃.

Or, aiming at the published genome sequence of the new coronavirus, selecting a relatively conservative and specific region near a 501-crRNA-W/M target point as a primer of RT-PCR, wherein the RT-PCR primer is a sequence which is obtained by counting the mutation frequency of each base through high-throughput sequence alignment of the new coronavirus, and the screened mutation frequency is low (less than one ten thousandth). And then according to the design principle of RT-PCR primers, sequences with good amplification efficiency and high specificity are obtained by screening and verifying from the specific sequences with low mutation frequency and are used as RT-PCR primers, and SEQ ID NO: 5 to 6.

The pretreatment method of the nucleic acid sample to be detected is that 18.5 mu L of sample solution is subjected to RT-PCR amplification, and the obtained amplification product is the processed nucleic acid sample; the nucleic acid sample to be tested is in this example an in vitro transcribed RNA molecule comprising a designed targeting fragment.

RT-PCR reaction system: 50 μ L of system, 400nM of upstream primer (501-RT-PCR-F), 400nM of downstream primer (501-RT-PCR-R), 25 μ L of 2 XBuffer mix (containing Buffer system and dNTP), 2.5 μ L of enzyme mix (containing reverse transcriptase, RNase inhibitor and DNA polymerase), and 18.5 μ L of test nucleic acid template.

RT-PCR reaction procedure: 30min at 50 ℃; 3min at 94 ℃; 30 cycles of 94 ℃ for 30s, 55 ℃ for 30s, and 72 ℃ for 30 s; 5min at 72 ℃; storing at 4 ℃.

(3) Design of reporter single stranded DNA molecules: 12-base random single-stranded DNA molecule 5 '-FAM-NNNNNNNNNNNN-BHQ 1-3' (SEQ ID NO: 8) with FAM and BHQ1 groups at both ends respectively.

(4) The 501-crRNA-W or 501-crRNA-M in-vitro transcription product, the processed nucleic acid sample, the LbaCas12a and the reporting single-stranded DNA molecule are mixed in a proper system in a proper proportion for reaction.

(5) The reaction system is as follows: 50nM LbaCas12a, 100nM 501-crRNA-W (or 501-crRNA-M), 500nM reporter single stranded DNA molecule, 10U RNase inhibitor (TaKaRa), 2.5. mu.L treated nucleic acid sample, 1 XNEBbuffer 2.1 in 20. mu.L system. The reaction system was reacted at 37 ℃ for 30 minutes.

(6) The reaction product was subjected to fluorescence excitation using excitation light of a wavelength of 492nm in a fluorescence detection device, and the fluorescence intensity was detected at a wavelength of 522nm to obtain a detection result.

(7) Taking RT-PCR amplification primers (SEQ ID NO: 5-6) as an example, the results are shown in FIG. 2, which shows that the concentration of the target nucleic acid is 10^-16M and above by this assayThe method can effectively distinguish the non-mutation N501 type new coronavirus from the mutation Y501 type new coronavirus.

(8) Taking RT-RAA amplification primers (SEQ ID NOS: 3-4) as an example, the results are shown in FIG. 3, which indicates that the concentration of the target nucleic acid is 10^-16M and above can effectively distinguish non-mutation N501 type and mutation Y501 type new coronavirus through the detection method.

Example 2:

in the embodiment of the invention, the CRISPR/Cas12a technology-based method for rapidly detecting the characteristic sequence nucleic acid of the non-mutant and mutant strains of the novel coronavirus is used for non-diagnosis or treatment purposes and comprises the following steps:

(1) the characteristic 501-crRNA-W and 501-crRNA-M are designed respectively for the non-mutated N501 (codon AAT) and the mutated Y501 (codon TAT) of the new coronavirus (SARS-CoV-2), which are different from the conventional crRNA design, and are highly specific and highly sensitive sequences obtained by introducing mutation and screening, such as SEQ ID NOs: 1-2, then constructing transcription vectors of 501-crRNA-W and 501-crRNA-M, and then transcribing and purifying.

Specifically, the method for crRNA in vitro transcription comprises the following steps: the reaction was carried out for 16 hours at 37 ℃ in the following system: nuclean-free water was added to 20. mu.L each of 1.5. mu.L of NTP, 1.5. mu.L of 10 × reaction buffer, 1. mu.g of Template DNA, and 1.5. mu.L of T7 RNA Polymerase Mix.

Specifically, the purification method of the crRNA transcript comprises the following steps: after the transcription product was treated with DNaseI (TaKaRa) for 15 minutes, the transcribed crRNA was purified using NEB RNA clean Kit or other RNA purification Kit.

(2) Aiming at the published genome sequence of the new coronavirus, selecting a relatively conservative and specific region near a 501-crRNA-W/M target point as a primer of RT-RAA, wherein the RT-RAA primer is a sequence which is obtained by counting the mutation frequency of each base through high-throughput sequence comparison of the new coronavirus, and the screened mutation frequency is low (less than one thousandth). And according to the design principle of RT-RAA primers, sequences with good amplification efficiency and high specificity are obtained by screening and verifying the special sequences with low mutation frequency and are used as RT-RAA primers, and SEQ ID NO: 3 to 4.

The pretreatment method of the nucleic acid sample to be detected is to carry out RT-RAA amplification on 2 mu L of sample solution, and the obtained amplification product is the processed nucleic acid sample; the nucleic acid sample to be tested is in this example an in vitro transcribed RNA molecule comprising the designed targeting segment.

RT-RAA reaction system: in a 50-mu L system, 400nM of the upstream primer (501-RT-RAA-F), 400nM of the downstream primer (501-RT-RAA-R), 41.5 mu L of A Buffer and 2 mu L of the nucleic acid sample template to be detected are included. The above systems were mixed and added to lyophilized RT-RAA reaction microspheres, magnesium acetate MgAc 280mM 2.5. mu.L was added and the reaction was started at 37 ℃.

Or, aiming at the published genome sequence of the new coronavirus, selecting a relatively conservative and specific region near a 501-crRNA-W/M target point as a primer of RT-PCR, wherein the RT-PCR primer is a sequence which is obtained by counting the mutation frequency of each base through high-throughput sequence alignment of the new coronavirus, and the screened mutation frequency is low (less than one ten thousandth). And then according to the design principle of RT-PCR primers, sequences with good amplification efficiency and high specificity are obtained by screening and verifying from the specific sequences with low mutation frequency and are used as RT-PCR primers, and SEQ ID NO: 5 to 6.

The pretreatment method of the nucleic acid sample to be detected is that 18.5 mu L of sample solution is subjected to RT-PCR amplification, and the obtained amplification product is the processed nucleic acid sample; the nucleic acid sample to be tested is in this example an in vitro transcribed RNA molecule comprising a designed targeting fragment.

RT-PCR reaction system: 50 μ L of system, 400nM of upstream primer (501-RT-PCR-F), 400nM of downstream primer (501-RT-PCR-R), 25 μ L of 2 XBuffer mix (containing Buffer system and dNTP), 2.5 μ L of enzyme mix (containing reverse transcriptase, RNase inhibitor and DNA polymerase), and 18.5 μ L of test nucleic acid template.

RT-PCR reaction procedure: 30min at 50 ℃; 3min at 94 ℃; 30 cycles of 94 ℃ for 30s, 55 ℃ for 30s, and 72 ℃ for 30 s; 5min at 72 ℃; storing at 4 ℃.

(3) Design of reporter single stranded DNA molecules: 12-base random single-stranded DNA molecule 5 '-Digoxin-NNNNNNNNNNNN-Biotin-3' (SEQ ID NO: 7) with Digoxin and Biotin groups at both ends, respectively.

(4) The 501-crRNA-W or 501-crRNA-M in-vitro transcription product, the processed nucleic acid sample, the LbaCas12a and the reporting single-stranded DNA molecule are mixed in a proper system in a proper proportion for reaction.

(5) The reaction system is as follows: 50nM LbaCas12a, 100nM 501-crRNA-W (or 501-crRNA-M), 2nM reporter single stranded DNA molecule, 10U RNase inhibitor (TaKaRa), 5. mu.L treated nucleic acid sample, 1 XNEBbuffer 2.1 in 40. mu.L system. The reaction system was reacted at 37 ℃ for 30 minutes.

(6) And soaking the lateral flow immunochromatography test paper sample loading area into the reaction mixed liquid, incubating for 5min at room temperature, and reading the test paper strip by naked eyes to obtain a detection result.

(7) Taking RT-PCR amplification primers (SEQ ID NO: 5-6) as an example, the results are shown in FIG. 4, which shows that the concentration of the target nucleic acid is 10^-15M and above, N501 non-mutant type and Y501 mutant type new coronavirus can be effectively distinguished by the detection method.

(8) Taking RT-RAA amplification primers (SEQ ID NOS: 3-4) as an example, the results are shown in FIG. 5, which indicates that the concentration of the target nucleic acid is 10^-15M and above, N501 non-mutant type and Y501 mutant type new coronavirus can be effectively distinguished by the detection method.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Sequence listing

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