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FEMS Microbiol Rev. 2015 May;39(3):428-41. doi: 10.1093/femsre/fuv023. Epub 2015 May 19.

Biogenesis pathways of RNA guides in archaeal and bacterial CRISPR-Cas adaptive immunity.

Author information

1
Helmholtz Centre for Infection Research, Department of Regulation in Infection Biology, Braunschweig 38124, Germany The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå Centre for Microbial Research (UCMR), Department of Molecular Biology, Umeå University, Umeå 90187, Sweden Hannover Medical School, Hannover 30625, Germany emmanuelle.charpentier@helmholtz-hzi.de.
2
Helmholtz Centre for Infection Research, Department of Regulation in Infection Biology, Braunschweig 38124, Germany.
3
Laboratory of Microbiology, Wageningen University, Wageningen 6703 HB, the Netherlands.
4
Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9ST, UK.

Abstract

CRISPR-Cas is an RNA-mediated adaptive immune system that defends bacteria and archaea against mobile genetic elements. Short mature CRISPR RNAs (crRNAs) are key elements in the interference step of the immune pathway. A CRISPR array composed of a series of repeats interspaced by spacer sequences acquired from invading mobile genomes is transcribed as a precursor crRNA (pre-crRNA) molecule. This pre-crRNA undergoes one or two maturation steps to generate the mature crRNAs that guide CRISPR-associated (Cas) protein(s) to cognate invading genomes for their destruction. Different types of CRISPR-Cas systems have evolved distinct crRNA biogenesis pathways that implicate highly sophisticated processing mechanisms. In Types I and III CRISPR-Cas systems, a specific endoribonuclease of the Cas6 family, either standalone or in a complex with other Cas proteins, cleaves the pre-crRNA within the repeat regions. In Type II systems, the trans-acting small RNA (tracrRNA) base pairs with each repeat of the pre-crRNA to form a dual-RNA that is cleaved by the housekeeping RNase III in the presence of the protein Cas9. In this review, we present a detailed comparative analysis of pre-crRNA recognition and cleavage mechanisms involved in the biogenesis of guide crRNAs in the three CRISPR-Cas types.

KEYWORDS:

Cas5d; Cas6; Cas9; RNase III; crRNA biogenesis; tracrRNA

PMID:
25994611
PMCID:
PMC5965381
DOI:
10.1093/femsre/fuv023
[Indexed for MEDLINE]
Free PMC Article

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