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Cell. 2016 Feb 11;164(4):710-21. doi: 10.1016/j.cell.2015.12.053. Epub 2016 Feb 4.

Degradation of Phage Transcripts by CRISPR-Associated RNases Enables Type III CRISPR-Cas Immunity.

Author information

1
Laboratory of Bacteriology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
2
Laboratory of Bacteriology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA. Electronic address: marraffini@rockefeller.edu.

Abstract

Type III-A CRISPR-Cas systems defend prokaryotes against viral infection using CRISPR RNA (crRNA)-guided nucleases that perform co-transcriptional cleavage of the viral target DNA and its transcripts. Whereas DNA cleavage is essential for immunity, the function of RNA targeting is unknown. Here, we show that transcription-dependent targeting results in a sharp increase of viral genomes in the host cell when the target is located in a late-expressed phage gene. In this targeting condition, mutations in the active sites of the type III-A RNases Csm3 and Csm6 lead to the accumulation of the target phage mRNA and abrogate immunity. Csm6 is also required to provide defense in the presence of mutated phage targets, when DNA cleavage efficiency is reduced. Our results show that the degradation of phage transcripts by CRISPR-associated RNases ensures robust immunity in situations that lead to a slow clearance of the target DNA.

PMID:
26853474
PMCID:
PMC4752873
DOI:
10.1016/j.cell.2015.12.053
[Indexed for MEDLINE]
Free PMC Article

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