In molecular biology, trans-activating crRNA (tracrRNA) is a small trans-encoded RNA. It was first discovered in the human pathogen Streptococcus pyogenes. In bacteria and archaea; CRISPR/Cas (clustered, regularly interspaced short palindromic repeats/CRISPR-associated proteins) constitute an RNA-mediated defense system which 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. There are several pathways of CRISPR activation, one of which requires a tracrRNA which plays a role in the maturation of crRNA. 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.
- 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): 602–7. doi:10.1038/nature09886. PMC 3070239. PMID 21455174.
- Terns MP, Terns RM (2011). "CRISPR-based adaptive immune systems". Curr Opin Microbiol. 14 (3): 321–7. doi:10.1016/j.mib.2011.03.005. PMC 3119747. PMID 21531607.
- 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): 816–21. doi:10.1126/science.1225829. PMID 22745249.
- Brouns SJ (2012). "A swiss army knife of immunity". Science. 337 (6096): 808–9. doi:10.1126/science.1227253. PMID 22904002.