阅读说明：本技术 利用修饰的单链核酸进行靶核酸检测的方法 (Method for detecting target nucleic acid using modified single-stranded nucleic acid ) 是由 梁亚峰 于 2020-06-16 设计创作，主要内容包括：本发明提供了利用修饰的单链核酸进行靶核酸检测的方法,具体地,涉及一种利用修饰的单链核酸进行靶核酸检测的方法、系统和试剂盒,所述的检测方法包括向含有靶核酸的反应体系中加入gRNA、Cas蛋白和单链核酸检测器,所述单链核酸检测器存在碱基修饰。(The invention provides a method for detecting a target nucleic acid by using a modified single-stranded nucleic acid, and particularly relates to a method, a system and a kit for detecting the target nucleic acid by using the modified single-stranded nucleic acid.)

1. A method of detecting a target nucleic acid in a sample, comprising contacting the sample with a V-type Cas protein (CRISPR/Cas effector protein), a gRNA (guide RNA) comprising a region that binds to the V-type Cas protein and a guide sequence that hybridizes to the target nucleic acid, and a single-stranded nucleic acid detector; detecting a detectable signal generated by the V-type Cas protein cleavage single-stranded nucleic acid detector, thereby detecting the target nucleic acid; the single-stranded nucleic acid detector does not hybridize to the gRNA;

the single-stranded nucleic acid detector comprises a plurality of nucleotides in which consecutive bases are guanine (G), and one or more guanines in the single-stranded nucleic acid detector have a base modification;

the base modification is a deamination modification to guanine.

2. The method according to claim 1, wherein the single-stranded nucleic acid detector is composed of a plurality of nucleotides whose consecutive bases are guanine (G).

3. The method of claim 1 or 2, wherein the single-stranded nucleic acid detector consists of at least 4 consecutive nucleotides whose bases are guanine (G) nucleotides, and wherein the presence of base modifications in one or more guanines in the single-stranded nucleic acid detector results in the absence of 2 or more consecutive nucleotides whose unmodified bases are guanine (G) from the single-stranded nucleic acid detector.

4. The method of any one of claims 1 to 3, wherein all guanines in the single stranded nucleic acid detector are deaminated.

5. The method of any one of claims 1-4, wherein the guanine is deaminated to form hypoxanthine (I).

6. The method of claim 1, wherein the V-type Cas protein is selected from any one or any combination of Cas12, Cas14 family proteins; preferably, the Cas14 family protein is selected from one or any combination of Cas14a and Cas14 b; more preferably, the Cas12 family protein is one or a combination of any two of Cas12i, Cas12j, Cas12a and Cas12 b.

7. The method of claim 1, wherein the detectable signal is detected by: vision-based detection, sensor-based detection, color detection, gold nanoparticle-based detection, fluorescence polarization, colloidal phase transition/dispersion, electrochemical detection, and semiconductor-based detection.

8. The method according to claim 1, wherein the target nucleic acid is a viral nucleic acid, a bacterial nucleic acid, a disease-related specific nucleic acid or a control-differentiated specific nucleic acid, preferably the disease-related specific nucleic acid is a specific mutation site or SNP site; preferably, the virus is a plant virus or an animal virus, e.g., papilloma virus, hepatic DNA virus, herpes virus, adenovirus, poxvirus, parvovirus, coronavirus; preferably, the virus is a coronavirus, e.g., SARS-CoV2(COVID-19), HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1, Mers-CoV.

9. A system or composition or kit for detecting a target nucleic acid in a sample, characterized in that the system or composition comprises a V-type Cas protein, a gRNA and a single-stranded nucleic acid detector as claimed in any one of claims 1-8.

10. Use of the system or composition or kit of claim 9 for detecting a target nucleic acid in a sample.

Technical Field

The present invention relates to the field of nucleic acid detection, and relates to methods for detecting target nucleic acids using modified single-stranded nucleic acids, and more particularly to methods, systems, and kits for detecting target nucleic acids using modified single-stranded nucleic acids.

Background

The method for specifically detecting Nucleic acid molecules (Nucleic acid detection) has important application values, such as pathogen detection, genetic disease detection and the like. In the aspect of pathogen detection, each pathogenic microorganism has a unique characteristic nucleic acid molecule sequence, so that nucleic acid molecule detection for a specific species, also called Nucleic Acid Diagnostics (NADs), can be developed, and is important in the fields of food safety, detection of environmental microbial contamination, infection of human pathogenic bacteria, and the like. Another aspect is the detection of Single Nucleotide Polymorphisms (SNPs) in humans or other species. Understanding the relationship between genetic variation and biological functions at the genomic level provides a new perspective for modern molecular biology, and SNPs are closely related to biological functions, evolution, diseases and the like, so the development of detection and analysis techniques of SNPs is particularly important.

The detection of specific nucleic acid molecules established today usually requires two steps, the first step being the amplification of the nucleic acid of interest and the second step being the detection of the nucleic acid of interest. The existing detection technologies include restriction endonuclease methods, Southern, Northern, dot blot, fluorescent PCR detection technologies, LAMP loop-mediated isothermal amplification technologies, recombinase polymerase amplification technologies (RPA) and the like. After 2012, CRISPR gene editing technology arose, a new nucleic acid diagnosis technology (SHERLOCK technology) of targeted RNA with Cas13 as a core was developed by the zhanfeng team based on RPA technology, a diagnosis technology (DETECTR technology) with Cas12 enzyme as a core was developed by the Doudna team, and a new nucleic acid detection technology (HOLMES technology) based on Cas12 was also developed by the royal doctor of the institute of physiology and ecology of plants in the shanghai of the chinese academy of sciences. Nucleic acid detection techniques developed based on CRISPR technology are playing an increasingly important role.

In the CRISPR-based nucleic acid detection technology, a nucleic acid probe or a nucleic acid detector is a key element of the detection technology, and the invention improves the nucleic acid probe, thereby expanding the application range of the technology.

Disclosure of Invention

The present invention provides methods, systems and kits for target nucleic acid detection using modified single stranded nucleic acids.

In one aspect, the invention provides a method of detecting a target nucleic acid in a sample, the method comprising contacting the sample with a type V CRISPR/CAS effector protein, a gRNA (guide RNA) comprising a region that binds to the CRISPR/CAS effector protein and a guide sequence that hybridizes to the target nucleic acid, and a single-stranded nucleic acid detector; detecting a detectable signal generated by the CRISPR/CAS effector protein cleavage single-stranded nucleic acid detector, thereby detecting the target nucleic acid.

In another aspect, the present invention also provides a system or composition for detecting a target nucleic acid in a sample, the system or composition comprising a type V CRISPR/CAS effector protein, a gRNA (guide RNA) comprising a region that binds to the CRISPR/CAS effector protein and a guide sequence that hybridizes to the target nucleic acid, and a single-stranded nucleic acid detector.

In another aspect, the present invention also provides a kit for detecting a target nucleic acid in a sample, the kit comprising a CRISPR/CAS effector protein of type V, a gRNA (guide RNA) comprising a region binding to the CRISPR/CAS effector protein and a guide sequence hybridizing to the target nucleic acid, and a single-stranded nucleic acid detector.

In another aspect, the invention also provides the use of the above system or kit for detecting a target nucleic acid in a sample.

In another aspect, the invention also provides the use of a type V CRISPR/CAS effector protein for detecting a target nucleic acid in a sample.

As described above, the type V CRISPR/CAS effector protein, upon binding or hybridization to a target nucleic acid in a sample, can cleave a single-stranded nucleic acid detector in a system.

In another aspect, the invention also provides the use of a type V CRISPR/CAS effector protein in the preparation of a reagent for detecting a target nucleic acid in a sample.

In the present invention, the single-stranded nucleic acid detector includes a single-stranded DNA, a single-stranded RNA, or a single-stranded DNA-RNA hybrid. In other embodiments, the single-stranded nucleic acid detector comprises a mixture of any two or three of single-stranded DNA, single-stranded RNA, or single-stranded DNA-RNA hybrids, e.g., a combination of single-stranded DNA and single-stranded RNA, a combination of single-stranded DNA and single-stranded DNA-RNA hybrids, and a combination of single-stranded RNA and single-stranded DNA-RNA.

In a preferred embodiment, the single stranded nucleic acid detector is a single stranded oligonucleotide detector.

The single-stranded nucleic acid detector does not hybridize to the gRNA.

In the present invention, the single-stranded nucleic acid detector comprises a plurality of nucleotides in which consecutive bases are guanine (G); and, one or more guanines in the single-stranded nucleic acid detector have a base modification; the base modification is a deamination modification to guanine. In other embodiments, the base modification may also be one or more of a methylation, acetylation, hydrogenation, fluorination, or sulfurization modification to guanine.

In a preferred embodiment, the single-stranded nucleic acid detector of the present invention is composed of a plurality of nucleotides in which consecutive bases are guanine (G); for example, at least 4 or more nucleotides in which the consecutive bases are guanine (G), e.g., 5 to 100, preferably 5 to 50, 5 to 20, e.g., 5, 6, 7, 8, 9, 10 or more, are included.

In the present invention, one or more guanines in the single-stranded nucleic acid detector are base-modified so that 2 or more consecutive nucleotides in which the unmodified base is guanine (G) are not present in the single-stranded nucleic acid detector; in other embodiments, the single stranded nucleic acid detector is such that there are no 3 or more consecutive nucleotides in which the unmodified base is guanine (G); alternatively, the single-stranded nucleic acid detector is absent of 4 or more consecutive nucleotides in which the unmodified base is guanine (G).

In a preferred embodiment, all guanines in the single stranded nucleic acid detector have a deamination modification; preferably, the guanine is deaminated and modified to hypoxanthine (I).

In a preferred embodiment, the single-stranded nucleic acid detector comprises a plurality of consecutive nucleotides whose bases are hypoxanthine (I); or, consists of a plurality of consecutive nucleotides of which the bases are hypoxanthine (I); preferably, it consists of at least 2, 3, 4, 5, 6, 7, 8, 9, 10 or more consecutive nucleotides of which the base is hypoxanthine (I).

Further, the V-type CRISPR/CAS effector protein is selected from CAS12, CAS14 family protein or a mutant thereof; in one embodiment, the Cas protein is preferably a Cas12 family, including but not limited to one or any several of Cas12a, Cas12b, Cas12i, Cas12 j; the Cas14 family protein is selected from Cas14a and/or Cas14 b.

In one embodiment, the Cas12a is selected from one or any of FnCas12a, assas 12a, LbCas12a, Lb5Cas12a, HkCas12a, OsCas12a, TsCas12a, BbCas12a, BoCas12a or Lb4Cas12 a; the Cas12a is preferably LbCas12a, the amino acid sequence is shown as SEQ ID No.1, or the derivative protein which is formed by substituting, deleting or adding one or more (such as 2, 3, 4, 5, 6, 7, 8, 9 or 10) amino acid residues of the amino acid sequence shown as SEQ ID No.1 or an active fragment thereof and has basically the same function.

In other embodiments, the amino acid sequence of Cas12b is as shown in SEQ ID No.2, or a derivative protein formed by substituting, deleting or adding one or more (e.g., 2, 3, 4, 5, 6, 7, 8, 9 or 10) amino acid residues of the amino acid sequence shown in SEQ ID No.2 or an active fragment thereof, and having substantially the same function.

In preferred embodiments, the amino acid sequence of the Cas12i protein is selected from the group consisting of:

(1) a protein shown as SEQ ID No. 3;

(2) derived protein formed by substituting, deleting or adding one or more (such as 2, 3, 4, 5, 6, 7, 8, 9 or 10) amino acid residues of the amino acid sequence shown in SEQ ID No.3 or active fragment thereof and having basically the same function.

The amino acid sequence of the Cas12j protein is selected from the group consisting of:

(1) a protein shown as SEQ ID No. 4;

(2) derived protein formed by substituting, deleting or adding one or more (such as 2, 3, 4, 5, 6, 7, 8, 9 or 10) amino acid residues of the amino acid sequence shown in SEQ ID No.4 or active fragment thereof and having basically the same function.

In one embodiment, the Cas protein mutant comprises amino acid substitutions, deletions or substitutions, and the mutant retains at least its trans cleavage activity. Preferably, the mutant has Cis and trans cleavage activity.

In the present invention, the target nucleic acid includes ribonucleotide or deoxyribonucleotide, and includes single-stranded nucleic acid, double-stranded nucleic acid, such as single-stranded DNA, double-stranded DNA, single-stranded RNA, double-stranded RNA.

In the present invention, the detectable signal is realized by: vision-based detection, sensor-based detection, color detection, gold nanoparticle-based detection, fluorescence polarization, colloidal phase transition/dispersion, electrochemical detection, and semiconductor-based detection.

In some embodiments, the methods of the invention further comprise the step of measuring a detectable signal produced by the CRISPR/CAS effector protein (CAS protein). The Cas protein, upon recognition or hybridization to the target nucleic acid, can activate the cleavage activity of single-stranded nucleic acid, thereby cleaving the single-stranded nucleic acid detector and thereby generating a detectable signal.

In the present invention, the detectable signal may be any signal generated when the single-stranded nucleic acid detector is cleaved. For example, detection based on gold nanoparticles, fluorescence polarization, colloidal phase transition/dispersion, electrochemical detection, semiconductor-based sensing. The detectable signal may be read by any suitable means, including but not limited to: measurement of a detectable fluorescent signal, gel electrophoresis detection (by detecting a change in a band on the gel), detection of the presence or absence of a color based on vision or a sensor, or a difference in the presence of a color (e.g., based on gold nanoparticles) and a difference in an electrical signal.

In a preferred embodiment, the detectable signal is achieved by: the 5 'end and the 3' end of the single-stranded nucleic acid detector are respectively provided with different reporter groups, and when the single-stranded nucleic acid detector is cut, a detectable reporter signal can be shown; for example, a single-stranded nucleic acid detector having a fluorophore and a quencher disposed at opposite ends thereof, when cleaved, can exhibit a detectable fluorescent signal.

In one embodiment, the fluorescent group is selected from one or any of FAM, FITC, VIC, JOE, TET, CY3, CY5, ROX, Texas Red or LC Red 460; the quenching group is selected from one or more of BHQ1, BHQ2, BHQ3, Dabcy1 or Tamra.

In other embodiments, the detectable signal may also be achieved by: the 5 'end and the 3' end of the single-stranded nucleic acid detector are respectively provided with different marker molecules, and a reaction signal is detected in a colloidal gold detection mode.

In one embodiment, the target nucleic acid comprises DNA, RNA, preferably single-stranded nucleic acid or double-stranded nucleic acid or nucleic acid modification.

In one embodiment, the target nucleic acid is derived from a sample of a virus, bacterium, microorganism, soil, water source, human, animal, plant, or the like. Preferably, the target nucleic acid is a product enriched or amplified by PCR, NASBA, RPA, SDA, LAMP, HAD, NEAR, MDA, RCA, LCR, RAM and the like.

In one embodiment, the method further comprises the step of obtaining the target nucleic acid from the sample.

In one embodiment, the target nucleic acid is a viral nucleic acid, a bacterial nucleic acid, a specific nucleic acid associated with a disease, such as a specific mutation site or SNP site or a nucleic acid that is different from a control; preferably, the virus is a plant virus or an animal virus, e.g., papilloma virus, hepatic DNA virus, herpes virus, adenovirus, poxvirus, parvovirus, coronavirus; preferably, the virus is a coronavirus, preferably SARS, SARS-CoV2(COVID-19), HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1, Mers-CoV.

In some embodiments, the target nucleic acid is derived from a cell, e.g., from a cell lysate.

In some embodiments, the measurement of the detectable signal may be quantitative, and in other embodiments, the measurement of the detectable signal may be qualitative.

Preferably, the single stranded nucleic acid detector produces a first detectable signal prior to cleavage by the Cas protein and produces a second detectable signal different from the first detectable signal after cleavage.

In the present invention, the gRNA includes a sequence (guide sequence) targeting the signature sequence to be detected and a sequence (direct repeat sequence or a portion thereof) that recognizes the Cas protein.

In the invention, the guide sequence comprises 10-40 bp; preferably, 12-25 bp; preferably, 15-23 bp; preferably, 16-18 bp.

In the present invention, the gRNA has at least 50% match with the signature sequence to be detected, preferably at least 60%, preferably at least 70%, preferably at least 80%, preferably at least 90%.

In one embodiment, the Cas protein and gRNA are used in a molar ratio of (0.8-1.2): 1.

in one embodiment, the Cas protein is used in a final concentration of 20-200nM, preferably, 30-100nM, more preferably, 40-80nM, more preferably, 50 nM.

In one embodiment, the gRNA is used in a final concentration of 20-200nM, preferably, 30-100nM, more preferably, 40-80nM, and more preferably, 50 nM.

In one embodiment, the target nucleic acid is used in a final concentration of 5-100nM, preferably, 10-50 nM.

In one embodiment, the single stranded nucleic acid detector is used at a final concentration of 100-.

In one embodiment, the single stranded nucleic acid detector has 2 to 300 nucleotides, preferably, 3 to 200 nucleotides, preferably, 3 to 100 nucleotides, preferably, 3 to 30 nucleotides, preferably, 4 to 20 nucleotides, more preferably, 5 to 15 nucleotides.

In one embodiment, the single stranded nucleic acid detector is a single stranded DNA molecule, a single stranded RNA molecule, or a single stranded DNA-RNA hybrid.

The terms "hybridize" or "complementary" or "substantially complementary" refer to a nucleic acid (e.g., RNA, DNA) that comprises a nucleotide sequence that enables it to bind non-covalently, i.e., to form base pairs and/or G/U base pairs with another nucleic acid in a sequence-specific, antiparallel manner (i.e., the nucleic acid binds specifically to the complementary nucleic acid), "anneal" or "hybridize". Hybridization requires that the two nucleic acids contain complementary sequences, although mismatches between bases are possible. Suitable conditions for hybridization between two nucleic acids depend on the length and degree of complementarity of the nucleic acids, variables well known in the art. Typically, the length of the hybridizable nucleic acid is 8 nucleotides or more (e.g., 10 nucleotides or more, 12 nucleotides or more, 15 nucleotides or more, 20 nucleotides or more, 22 nucleotides or more, 25 nucleotides or more, or 30 nucleotides or more).

It is understood that the sequence of a polynucleotide need not be 100% complementary to the sequence of its target nucleic acid to specifically hybridize. A polynucleotide may comprise 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, 98% or more, 99% or more, 99.5% or more, or a target region that hybridizes thereto has 100% sequence complementarity of the target region.

General definition:

unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

The term "amino acid" refers to a carboxylic acid containing an amino group. Each protein in an organism is composed of 20 basic amino acids.

The terms "polynucleotide", "nucleotide sequence", "nucleic acid molecule" and "nucleic acid" are used interchangeably and include DNA, RNA or hybrids thereof, whether double-stranded or single-stranded.

The term "oligonucleotide" refers to a sequence of 3 to 100 nucleotides, preferably 3 to 30 nucleotides, preferably 4 to 20 nucleotides, more preferably 5 to 15 nucleotides.

The term "homology" or "identity" is used to refer to a sequence between two polypeptides or between two nucleic acids

And (4) matching the situation. When two sequences to be compared are substituted by the same base or amino acid monomer at a position

When a subunit is occupied (e.g., a position in each of two DNA molecules is occupied by adenine,

or a position in each of the two polypeptides is occupied by a lysine), then the respective molecule is at that position

Are identical. Between the two sequences. Typically, this is done when the two sequences are aligned to yield maximum identity

And (6) comparing. Such an alignment can be determined by using, for example, the identity of the amino acid sequences by conventional methods, as taught by, for example, Smith and Waterman,1981, adv.Appl.Math.2:482Pearson & Lipman,1988, Proc.Natl.Acad.Sci.USA 85:2444, Thompson et al, 1994, Nucleic Acids Res 22:467380, etc., by computerized operational algorithms (GAP, BESTFIT, FASTA, and TFASTA, Genetics Computer Group in the Wisconsin Genetics software package). The BLAST algorithm, available from the national center for Biotechnology information (NCBI www.ncbi.nlm.nih.gov /), can also be used, determined using default parameters.

As used herein, the "CRISPR" refers to clustered, regularly interspaced short palindromic repeats (clustered regularly interspaced short palindromic repeats) derived from the immune system of a microorganism.

As used herein, "biotin", also known as vitamin H, is a small molecule vitamin with a molecular weight of 244 Da. "avidin", also called avidin, is a basic glycoprotein having 4 binding sites with extremely high affinity to biotin, and streptavidin is a commonly used avidin. The very strong affinity of biotin to avidin can be used to amplify or enhance the detection signal in the detection system. For example, biotin is easily bonded to a protein (such as an antibody) by a covalent bond, and an avidin molecule bonded to an enzyme reacts with a biotin molecule bonded to a specific antibody, so that not only is a multi-stage amplification effect achieved, but also color is developed due to the catalytic effect of the enzyme when the enzyme meets a corresponding substrate, and the purpose of detecting an unknown antigen (or antibody) molecule is achieved.

Target nucleic acid

As used herein, the "target nucleic acid" refers to a polynucleotide molecule extracted from a biological sample (sample to be tested). The biological sample is any solid or fluid sample obtained, excreted or secreted from any organism, including but not limited to single-celled organisms such as bacteria, yeasts, protozoa and amoebae and the like, multicellular organisms (e.g. plants or animals, including samples from healthy or superficially healthy human subjects or human patients affected by a condition or disease to be diagnosed or investigated, e.g. infection by a pathogenic microorganism such as a pathogenic bacterium or virus). For example, the biological sample may be a biological fluid obtained from, for example, blood, plasma, serum, urine, feces, sputum, mucus, lymph, synovial fluid, bile, ascites, pleural effusion, seroma, saliva, cerebrospinal fluid, aqueous or vitreous humor, or any bodily secretion, exudate (e.g., obtained from an abscess or any other site of infection or inflammation), or a fluid obtained from a joint (e.g., a normal joint or a joint affected by a disease, such as rheumatoid arthritis, osteoarthritis, gout, or septic arthritis), or a swab of a skin or mucosal surface. The sample may also be a sample obtained from any organ or tissue (including biopsies or autopsy specimens, e.g., tumor biopsies) or may comprise cells (primary cells or cultured cells) or culture medium conditioned by any cell, tissue or organ. Exemplary samples include, but are not limited to, cells, cell lysates, blood smears, cytocentrifuge preparations, cytological smears, bodily fluids (e.g., blood, plasma, serum, saliva, sputum, urine, bronchoalveolar lavage, semen, etc.), tissue biopsies (e.g., tumor biopsies), fine needle aspirates, and/or tissue sections (e.g., cryostat tissue sections and/or paraffin-embedded tissue sections).

In other embodiments, the biological sample may be a plant cell, callus, tissue or organ (e.g., root, stem, leaf, flower, seed, fruit), and the like.

In the present invention, the target nucleic acid also includes a DNA molecule formed by reverse transcription of RNA, and further, the target nucleic acid can be amplified by a technique known in the art, such as isothermal amplification techniques, such as nucleic acid sequencing-based amplification (NASBA), Recombinase Polymerase Amplification (RPA), loop-mediated isothermal amplification (LAMP), Strand Displacement Amplification (SDA), helicase-dependent amplification (HDA), or Nicking Enzyme Amplification (NEAR), and non-isothermal amplification techniques. In certain exemplary embodiments, non-isothermal amplification methods may be used, including, but not limited to, PCR, Multiple Displacement Amplification (MDA), Rolling Circle Amplification (RCA), Ligase Chain Reaction (LCR), or derivative amplification methods (RAM).

Further, the detection method of the present invention further comprises a step of amplifying the target nucleic acid; the detection system further comprises a reagent for amplifying the target nucleic acid. The reagents for amplification include one or more of the following: DNA polymerase, strand displacing enzyme, helicase, recombinase, single-strand binding protein, and the like.

Cas protein

As used herein, "Cas protein" refers to a CRISPR-associated protein, preferably from type V or type VI CRISPR/Cas protein, which upon binding to a signature sequence (target sequence) to be detected (i.e., forming a ternary complex of Cas protein-gRNA-target sequence) can induce its trans activity, i.e., random cleavage of non-targeted single-stranded nucleotides (i.e., the single-stranded nucleic acid detector described herein, preferably single-stranded DNA (ssdna), single-stranded DNA-RNA hybrids, single-stranded RNA). When the Cas protein is combined with the characteristic sequence, the protein can induce the trans activity by cutting or not cutting the characteristic sequence; preferably, it induces its trans activity by cleaving the signature sequence; more preferably, it induces its trans activity by cleaving the single-stranded signature sequence. The Cas protein recognizes the characteristic sequence by recognizing PAM (protospacer adjacenttoment motif) adjacent to the characteristic sequence.

The Cas protein is a protein at least having trans cleavage activity, and preferably, the Cas protein is a protein having Cis and trans cleavage activity. The Cis activity refers to the activity that the Cas protein can recognize a PAM site and specifically cut a target sequence under the action of the gRNA.

The Cas protein provided by the invention comprises V-type CRISPR/CAS effector proteins, including protein families such as Cas12 and Cas 14. Preferably, e.g., Cas12 proteins, e.g., Cas12a, Cas12b, Cas12i, Cas12 j; preferably, the Cas protein is Cas12a, Cas12b, Cas12i, Cas12 j; the Cas14 protein family includes Cas14a, Cas14b, and the like.

In embodiments, a Cas protein, as referred to herein, such as Cas12, also encompasses a functional variant of Cas or a homolog or ortholog thereof. As used herein, a "functional variant" of a protein refers to a variant of such a protein that at least partially retains the activity of the protein. Functional variants may include mutants (which may be insertion, deletion or substitution mutants), including polymorphs and the like. Also included in functional variants are fusion products of such proteins with another, usually unrelated, nucleic acid, protein, polypeptide or peptide. Functional variants may be naturally occurring or may be artificial. Advantageous embodiments may relate to engineered or non-naturally occurring V-type DNA targeting effector proteins.

In one embodiment, one or more nucleic acid molecules encoding a Cas protein, such as Cas12, or orthologs or homologs thereof, may be codon optimized for expression in a eukaryotic cell. Eukaryotes can be as described herein. One or more nucleic acid molecules may be engineered or non-naturally occurring.

In one embodiment, the Cas12 protein or ortholog or homolog thereof may comprise one or more mutations (and thus the nucleic acid molecule encoding it may have one or more mutations.

In one embodiment, the Cas protein may be from: cilium, listeria, corynebacterium, satrapia, legionella, treponema, Proteus, eubacterium, Streptococcus, Lactobacillus, Mycoplasma, Bacteroides, Flavivivola, Flavobacterium, Azospirillum, Sphaerochaeta, gluconacetobacter, Neisseria, Rochelia, Parvibaculum, Staphylococcus, Nitrarefactor, Mycoplasma, Campylobacter, and Muspirillum.

In one embodiment, the Cas protein is selected from the group consisting of proteins consisting of:

(1) proteins shown as SEQ ID No. 1-4;

(2) derived proteins which are formed by substituting, deleting or adding one or more (such as 2, 3, 4, 5, 6, 7, 8, 9 or 10) amino acid residues in the amino acid sequences shown in SEQ ID No.1-4 or active fragments thereof and have basically the same functions.

In one embodiment, the Cas protein further includes proteins having 50%, preferably 55%, preferably 60%, preferably 65%, preferably 70%, preferably 75%, preferably 80%, preferably 85%, preferably 90%, preferably 95%, sequence identity to the above sequences and having trans activity.

The Cas protein can be obtained by recombinant expression vector technology, namely, a nucleic acid molecule encoding the protein is constructed on a proper vector and then is transformed into a host cell, so that the encoding nucleic acid molecule is expressed in the cell, and the corresponding protein is obtained. The protein can be secreted by cells, or the protein can be obtained by breaking cells through a conventional extraction technology. The encoding nucleic acid molecule may or may not be integrated into the genome of the host cell for expression. The vector may further comprise regulatory elements which facilitate sequence integration, or self-replication. The vector may be, for example, of the plasmid, virus, cosmid, phage, etc. type, which are well known to those skilled in the art, and preferably, the expression vector of the present invention is a plasmid. The vector further comprises one or more regulatory elements selected from the group consisting of promoters, enhancers, ribosome binding sites for translation initiation, terminators, polyadenylation sequences, and selectable marker genes.

The host cell may be a prokaryotic cell, such as E.coli, Streptomyces, Agrobacterium: or lower eukaryotic cells, such as yeast cells; or higher eukaryotic cells, such as plant cells. It will be clear to one of ordinary skill in the art how to select an appropriate vector and host cell.

gRNA

As used herein, the "gRNA" is also referred to as guide RNA or guide RNA and has a meaning commonly understood by those skilled in the art. In general, the guide RNA may comprise, or consist essentially of, a direct repeat and a guide sequence (guidessequence), also referred to as a spacer (spacer) in the context of an endogenous CRISPR system. grnas may include crRNA and tracrRNA or only crRNA depending on Cas protein on which they depend in different CRISPR systems. The crRNA and tracrRNA may be artificially engineered to fuse to form single guide RNA (sgRNA). In certain instances, the guide sequence is any polynucleotide sequence that is sufficiently complementary to the target sequence (the signature sequence described in the present invention) to hybridize to the target sequence and direct specific binding of the CRISPR/Cas complex to the target sequence, typically having a sequence length of 12-25 nt. The direct repeat sequence can fold to form a specific structure (such as a stem-loop structure) for recognition by the Cas protein to form a complex. The targeting sequence need not be 100% complementary to the signature sequence (target sequence). The targeting sequence is not complementary to the single stranded nucleic acid detector.

In certain embodiments, the degree of complementarity (degree of match) between a targeting sequence and its corresponding target sequence is at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, or at least 99%, when optimally aligned. Determining the optimal alignment is within the ability of one of ordinary skill in the art. For example, there are published and commercially available alignment algorithms and programs such as, but not limited to, ClustalW, the Smith-Waterman algorithm in matlab (Smith-Waterman), Bowtie, Geneius, Biopython, and SeqMan.

The gRNA of the invention can be natural, and can also be artificially modified or designed and synthesized.

Single-stranded nucleic acid detector

The single-stranded nucleic acid detector of the present invention refers to a sequence containing 2 to 200 nucleotides, preferably, 2 to 150 nucleotides, preferably, 3 to 100 nucleotides, preferably, 3 to 30 nucleotides, preferably, 4 to 20 nucleotides, and more preferably, 5 to 15 nucleotides. Preferably a single-stranded DNA molecule, a single-stranded RNA molecule or a single-stranded DNA-RNA hybrid.

In the invention, the base of the single-stranded nucleic acid detector is modified, so that poly G which cannot be used for nucleic acid detection originally can be efficiently used for nucleic acid detection after modification.

The single-stranded nucleic acid detector is used in a detection method or system to report whether a characteristic sequence is contained. The single-stranded nucleic acid detector comprises different reporter groups or marker molecules at both ends, and does not present a reporter signal when in an initial state (i.e., an uncleaved state), and presents a detectable signal when the single-stranded nucleic acid detector is cleaved, i.e., presents a detectable difference after cleavage from before cleavage. In the present invention, if a detectable difference can be detected, it is reflected that the target nucleic acid contains a characteristic sequence to be detected; alternatively, if the detectable difference is not detectable, it indicates that the target nucleic acid does not contain the signature sequence to be detected.

In one embodiment, the reporter group or the marker molecule comprises a fluorescent group and a quenching group, wherein the fluorescent group is selected from one or any several of FAM, FITC, VIC, JOE, TET, CY3, CY5, ROX, Texas Red or LC RED 460; the quenching group is selected from one or more of BHQ1, BHQ2, BHQ3, Dabcy1 or Tamra.

In one embodiment, the single stranded nucleic acid detector has a first molecule (e.g., FAM or FITC) attached to the 5 'end and a second molecule (e.g., biotin) attached to the 3' end. The reaction system containing the single-stranded nucleic acid detector is matched with the flow strip to detect the characteristic sequence (preferably, a colloidal gold detection mode). The flow strip is designed with two capture lines, with an antibody that binds to a first molecule (i.e. a first molecular antibody) at the sample contacting end (colloidal gold), an antibody that binds to the first molecular antibody at the first line (control line), and an antibody that binds to a second molecule (i.e. a second molecular antibody, such as avidin) at the second line (test line). As the reaction flows along the strip, the first molecular antibody binds to the first molecule carrying the cleaved or uncleaved oligonucleotide to the capture line, the cleaved reporter will bind to the antibody of the first molecular antibody at the first capture line, and the uncleaved reporter will bind to the second molecular antibody at the second capture line. Binding of the reporter group at each line will result in a strong readout/signal (e.g. color). As more reporters are cut, more signal will accumulate at the first capture line and less signal will appear at the second line. In certain aspects, the invention relates to the use of a flow strip as described herein for detecting nucleic acids. In certain aspects, the invention relates to a method of detecting nucleic acids using a flow strip as defined herein, e.g. a (side) flow test or a (side) flow immunochromatographic assay. In some aspects, the molecules in the single-stranded nucleic acid detector may be replaced with each other, or the positions of the molecules may be changed, and the modified form is also included in the present invention as long as the reporting principle is the same as or similar to that of the present invention.

The detection method can be used for quantitative detection of the characteristic sequence to be detected. The quantitative detection index can be quantified according to the signal intensity of the reporter group, such as the luminous intensity of a fluorescent group, or the width of a color development strip.

Drawings

Figure 1. validation of Cas12a detection results using different single stranded DNAs as single stranded nucleic acid detectors.

FIG. 2 detection results using Cas12a with poly I as a single stranded nucleic acid detector; wherein line 1 is the test result of adding poly I detector, and line 2 is the control.

FIG. 3 detection results using Cas12b with poly I as a single stranded nucleic acid detector; wherein line 1 is the test result of adding poly I detector, and line 2 is the control.

FIG. 4 detection results using Cas12I with poly I as a single stranded nucleic acid detector; wherein line 1 is the test result of adding poly I detector, and line 2 is the control.

FIG. 5 detection results using Cas12j with poly I as a single stranded nucleic acid detector; wherein line 1 is the test result of adding poly I detector, and line 2 is the control.

Detailed description of the preferred embodiments

The present invention will be further described with reference to the following examples, which are intended to be illustrative only and not to be limiting of the invention in any way, and any person skilled in the art can modify the present invention by applying the teachings disclosed above and applying them to equivalent embodiments with equivalent modifications. Any simple modification or equivalent changes made to the following embodiments according to the technical essence of the present invention, without departing from the technical spirit of the present invention, fall within the scope of the present invention.

The technical scheme of the invention is based on the following principle, the nucleic acid of a sample to be detected is obtained, for example, a target nucleic acid can be obtained by an amplification method, and the gRNA which can be paired with the target nucleic acid is used for guiding the Cas protein to be identified and combined on the target nucleic acid; subsequently, the Cas protein activates single-stranded nucleic acid cleavage activity, thereby cleaving the single-stranded nucleic acid detector in the system; the two ends of the single-stranded nucleic acid detector are respectively provided with a fluorescent group and a quenching group, and if the single-stranded nucleic acid detector is cut, fluorescence can be excited; if the single-stranded nucleic acid cannot be cleaved, fluorescence is not excited; in other embodiments, both ends of the single-stranded nucleic acid detector may be provided with a label capable of being detected by colloidal gold.