{{Short description|RNA-targeting CRISPR effector}} '''Cas13''' is a CRISPR-associated enzyme that targets RNA. Unlike DNA-targeting Cas9 and Cas12, Cas13 utilizes a single RNA-guided endonuclease to bind and cleave specific RNA sequences. It employs two distinct ribonuclease activities: one for processing its own CRISPR RNA (crRNA) and another for degrading the target RNA.<ref name="Zhang_2020">{{cite journal | vauthors = Zhang J, You Y | title = CRISPR-Cas13a system: a novel approach to precision oncology | journal = Cancer Biology & Medicine | volume = 17 | issue = 1 | pages = 6–8 | date = February 2020 | pmid = 32296572 | pmc = 7142841 | doi = 10.20892/j.issn.2095-3941.2019.0325 }}</ref><ref name="Zhang_2024">{{cite journal | vauthors = Zhang Y, Li S, Li R, Qiu X, Fan T, Wang B, Zhang B, Zhang L | title = Advances in application of CRISPR-Cas13a system | journal = Frontiers in Cellular and Infection Microbiology | volume = 14 | issue = | article-number = 1291557 | date = 2024 | pmid = 38524179 | pmc = 10958658 | doi = 10.3389/fcimb.2024.1291557 | doi-access = free | url = }}</ref><ref name="Zhao_2022">{{cite journal | vauthors = Zhao L, Qiu M, Li X, Yang J, Li J | title = CRISPR-Cas13a system: A novel tool for molecular diagnostics | journal = Frontiers in Microbiology | volume = 13 | issue = | article-number = 1060947 | date = 2022 | pmid = 36569102 | pmc = 9772028 | doi = 10.3389/fmicb.2022.1060947 | doi-access = free | url = }}</ref>
The system's specificity allows for the correction of mutations at the transcript level. For example, it has been used to repair KRAS-G12D mRNA in pancreatic cancer models with high efficiency while minimizing effects on healthy cells.<ref name="Zhang_2020" /> It has been adapted into tools such as the REPAIR platform, which edits RNA bases to treat genetic disorders, including Usher syndrome, in animal models. Cas13 also possesses collateral RNA-cleavage activity, which is utilized in diagnostic platforms like SHERLOCK to detect pathogens, tumor DNA, and viral variants with high sensitivity.<ref name="Zhao_2022" /> Its PAM-independent targeting and reduced off-target effects make it suitable for RNA imaging, phage genome engineering, and transient gene regulation.<ref name="Zhang_2024" />
== History == In 2016, researchers in Feng Zhang's group at MIT and the Broad Institute characterized the nuclease {{visible anchor|Cas13a}} (formerly {{visible anchor|C2c2}}) from the bacterium ''Leptotrichia shahii''.<ref>{{cite journal | vauthors = Abudayyeh OO, Gootenberg JS, Konermann S, Joung J, Slaymaker IM, Cox DB, Shmakov S, Makarova KS, Semenova E, Minakhin L, Severinov K, Regev A, Lander ES, Koonin EV, Zhang F | title = C2c2 is a single-component programmable RNA-guided RNA-targeting CRISPR effector | journal = Science | volume = 353 | issue = 6299 | article-number = aaf5573 | date = August 2016 | pmid = 27256883 | pmc = 5127784 | doi = 10.1126/science.aaf5573 | bibcode = 2016Sci...353f5573A }}</ref> Its collateral cleavage property is central to several diagnostic technologies.<ref name="Nucleic acid detection with CRISPR">{{cite journal | vauthors = Gootenberg JS, Abudayyeh OO, Lee JW, Essletzbichler P, Dy AJ, Joung J, Verdine V, Donghia N, Daringer NM, Freije CA, Myhrvold C, Bhattacharyya RP, Livny J, Regev A, Koonin EV, Hung DT, Sabeti PC, Collins JJ, Zhang F | title = Nucleic acid detection with CRISPR-Cas13a/C2c2 | journal = Science | volume = 356 | issue = 6336 | pages = 438–442 | date = April 2017 | pmid = 28408723 | pmc = 5526198 | doi = 10.1126/science.aam9321 | bibcode = 2017Sci...356..438G }}</ref><ref>{{cite journal | vauthors = Gootenberg JS, Abudayyeh OO, Kellner MJ, Joung J, Collins JJ, Zhang F | title = Multiplexed and portable nucleic acid detection platform with Cas13, Cas12a, and Csm6 | journal = Science | volume = 360 | issue = 6387 | pages = 439–444 | date = April 2018 | pmid = 29449508 | pmc = 5961727 | doi = 10.1126/science.aaq0179 | bibcode = 2018Sci...360..439G }}</ref><ref name="SPRINT: a Cas13a-based platform for">{{cite journal | vauthors = Iwasaki RS, Batey RT | title = SPRINT: a Cas13a-based platform for detection of small molecules | journal = Nucleic Acids Research | volume = 48 | issue = 17 | pages = e101 | date = September 2020 | pmid = 32797156 | pmc = 7515716 | doi = 10.1093/nar/gkaa673 | doi-access = free }}</ref>
In 2018, a team led by Silvana Konermann and Patrick Hsu at the Salk Institute identified Cas13d, a compact subclass of RNA-targeting CRISPR effectors. An engineered variant of ''Ruminococcus flavefaciens'' Cas13d, named CasRx, demonstrated high efficiency and specificity in human cells compared to RNA interference. CasRx can be packaged into adeno-associated virus (AAV) vectors for transcriptome engineering and gene therapy.<ref name="CasRX">{{cite journal | vauthors = Konermann S, Lotfy P, Brideau NJ, Oki J, Shokhirev MN, Hsu PD | title = Transcriptome Engineering with RNA-Targeting Type VI-D CRISPR Effectors | journal = Cell | date = April 2018 | volume = 173 | issue = 3 | pages = 665–676.e14 | pmid = 29551272 | pmc = 5910255 | doi = 10.1016/j.cell.2018.02.033 | bibcode = 2018Cell..173..665K }}</ref>
In 2021, researchers characterized miniature Cas13 protein variants, Cas13X and Cas13Y. Studies using the SARS-CoV-2 N gene sequence as a target showed that mCas13, when coupled with RT-LAMP, detected SARS-CoV-2 in synthetic and clinical samples with high sensitivity and specificity, comparable to RT-qPCR.<ref>{{cite journal | vauthors = Mahas A, Wang Q, Marsic T, Mahfouz MM | title = A Novel Miniature CRISPR-Cas13 System for SARS-CoV-2 Diagnostics | journal = ACS Synthetic Biology | volume = 10 | issue = 10 | pages = 2541–2551 | date = October 2021 | pmid = 34546709 | pmc = 8482783 | doi = 10.1021/acssynbio.1c00181 }}</ref>
== Applications ==
Cas13 has been adapted to function as an RNA editor capable of correcting mutations without modifying DNA. The REPAIR system utilizes a catalytically inactive Cas13 (dCas13) that binds target RNA without cleaving it. This dCas13 is fused to the catalytic domain of ADAR2, an enzyme that converts adenosine (A) to inosine (I), which is interpreted by the cellular machinery as guanosine (G). This complex can be guided to specific mRNA locations to correct disease-causing mutations.<ref>{{Cite journal | vauthors = Gootenberg JS, Abudayyeh OO, Franklin B, Kellner MJ, Joung J, Zhang F, Cox DB | title = RNA editing with CRISPR-Cas13 | journal = Science | location = New York, N.Y. | volume = 358 | issue = 6366 | pages = 1019–1027 | date = 2017-11-24 | pmid = 29070703 | pmc = 5793859 | doi = 10.1126/science.aaq0180 | bibcode = 2017Sci...358.1019C }}</ref>
When combined with a high-fidelity ADAR2 variant, the REPAIR system has demonstrated the ability to edit targets with minimal off-target effects. In murine models of Usher syndrome, the dCas13–ADAR system, delivered via viral vectors, restored usherin protein levels, corrected defective transcripts, and improved vision. These results indicate that Cas13-mediated RNA editing may offer a viable approach for treating genetic disorders.<ref>{{Cite journal | vauthors = Major L, Salman A, McDermott LA, Yang J, King AJ, McClements ME, MacLaren RE, Fry LE | title = Comparison of CRISPR-Cas13b RNA base editing approaches for USH2A-associated inherited retinal degeneration | journal = Communications Biology | volume = 8 | issue = 1 | article-number = 200 | date = 2025-02-08 | pmid = 39922978 | pmc = 11807095 | doi = 10.1038/s42003-025-07557-3 | language = en | issn = 2399-3642 }}</ref>
Further refinements have led to the development of "dead" Cas13b, which retains binding capabilities but lacks cleavage activity. Paired with a guide RNA that includes a specific A-to-C mismatch at the target site, this system directs the ADAR2 enzyme to edit a single base. Initial tests in human cells showed reliable editing within a 30-nucleotide window with significant precision.<ref>{{Cite journal | vauthors = Lotfy P, Brideau NJ, Oki J, Shokhirev MN, Hsu PD, Konermann S | title = Transcriptome Engineering with RNA-Targeting Type VI-D CRISPR Effectors | journal = Cell | volume = 173 | issue = 3 | pages = 665–676.e14 | date = 2018-04-19 | pmid = 29551272 | pmc = 5910255 | doi = 10.1016/j.cell.2018.02.033 | bibcode = 2018Cell..173..665K | language = English | issn = 0092-8674 }}</ref>
==See also== *Mammoth Biosciences *Sherlock Biosciences
== References == {{Reflist}}
Category:Genetic engineering Category:Enzymes Category:Genome editing