Trans-activating crRNA

In molecular biology, trans-activating CRISPR RNA (tracrRNA) is a small trans-encoded RNA. It was first discovered by Emmanuelle Charpentier in her study of the human pathogen Streptococcus pyogenes. ^[1] In bacteria and archaea, CRISPR-Cas (clustered, regularly interspaced short palindromic repeats/CRISPR-associated proteins) constitute an RNA-mediated defense system that protects against viruses and plasmids. This defensive pathway has three steps. First, a copy of the invading nucleic acid is integrated into the CRISPR locus. Next, CRISPR RNAs (crRNAs) are transcribed from this CRISPR locus. The crRNAs are then incorporated into effector complexes, where the crRNA guides the complex to the invading nucleic acid and the Cas proteins degrade this nucleic acid. ^[2] There are several CRISPR system subtypes.

Type II CRISPR-Cas systems require a tracrRNA which plays a role in the maturation of crRNA. ^[3] The tracrRNA is partially complementary to and base pairs with a pre-crRNA forming an RNA duplex. This is cleaved by RNase III, an RNA-specific ribonuclease, to form a crRNA/tracrRNA hybrid. This hybrid acts as a guide for the endonuclease Cas9, which cleaves the invading nucleic acid. ^{[1] [4] [5]}

See also

• CRISPR

References

1. Deltcheva E, Chylinski K, Sharma CM, Gonzales K, Chao Y, Pirzada ZA, et al. (2011). "CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III". Nature. 471 (7340): 602–607. Bibcode:2011Natur.471..602D. doi:10.1038/nature09886. PMC   3070239 . PMID   21455174.
2. Terns MP, Terns RM (2011). "CRISPR-based adaptive immune systems". Curr Opin Microbiol. 14 (3): 321–327. doi:10.1016/j.mib.2011.03.005. PMC   3119747 . PMID   21531607.
3. Charpentier E, Richter H, van der Oost J, White MF (2015). "Biogenesis pathways of RNA guides in archaeal and bacterial CRISPR-Cas adaptive immunity". FEMS Microbiology Reviews. 39 (3): 428–441. doi:10.1093/femsre/fuv023. PMC   5965381 . PMID   25994611.
4. Jinek M, Chylinski K, Fonfara I, Hauer M, Doudna JA, Charpentier E (2012). "A Programmable Dual-RNA-Guided DNA Endonuclease in Adaptive Bacterial Immunity". Science. 337 (6096): 816–821. Bibcode:2012Sci...337..816J. doi:10.1126/science.1225829. PMC   6286148 . PMID   22745249.
5. Brouns SJ (2012). "A swiss army knife of immunity". Science. 337 (6096): 808–809. Bibcode:2012Sci...337..808B. doi:10.1126/science.1227253. PMID   22904002. S2CID   206543893.

Further reading

• Le Rhun A, Charpentier E (2012). "Small RNAs in streptococci". RNA Biol. 9 (4): 414–426. doi: 10.4161/rna.20104 . PMID   22546939.