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Nat Microbiol. 2016 Jun 13;1(8):16085. doi: 10.1038/nmicrobiol.2016.85.

Inactivation of CRISPR-Cas systems by anti-CRISPR proteins in diverse bacterial species.

Author information

1
Department of Biochemistry, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada.
2
Department of Microbiology and Immunology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
3
Department of Molecular Genetics, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada.
4
Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, 160 College Street, Toronto, Ontario M5S 3E1, Canada.

Abstract

CRISPR-Cas systems provide sequence-specific adaptive immunity against foreign nucleic acids(1,2). They are present in approximately half of all sequenced prokaryotes(3) and are expected to constitute a major barrier to horizontal gene transfer. We previously described nine distinct families of proteins encoded in Pseudomonas phage genomes that inhibit CRISPR-Cas function(4,5). We have developed a bioinformatic approach that enabled us to discover additional anti-CRISPR proteins encoded in phages and other mobile genetic elements of diverse bacterial species. We show that five previously undiscovered families of anti-CRISPRs inhibit the type I-F CRISPR-Cas systems of both Pseudomonas aeruginosa and Pectobacterium atrosepticum, and a dual specificity anti-CRISPR inactivates both type I-F and I-E CRISPR-Cas systems. Mirroring the distribution of the CRISPR-Cas systems they inactivate, these anti-CRISPRs were found in species distributed broadly across the phylum Proteobacteria. Importantly, anti-CRISPRs originating from species with divergent type I-F CRISPR-Cas systems were able to inhibit the two systems we tested, highlighting their broad specificity. These results suggest that all type I-F CRISPR-Cas systems are vulnerable to inhibition by anti-CRISPRs. Given the widespread occurrence and promiscuous activity of the anti-CRISPRs described here, we propose that anti-CRISPRs play an influential role in facilitating the movement of DNA between prokaryotes by breaching the barrier imposed by CRISPR-Cas systems.

PMID:
27573108
DOI:
10.1038/nmicrobiol.2016.85
[Indexed for MEDLINE]

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