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Annu Rev Virol. 2017 Sep 29;4(1):37-59. doi: 10.1146/annurev-virology-101416-041616. Epub 2017 Jul 27.

The Discovery, Mechanisms, and Evolutionary Impact of Anti-CRISPRs.

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Department of Microbiology and Immunology, University of California, San Francisco, California 94158; email:
Department of Molecular Genetics and Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.


Bacteria and archaea use CRISPR-Cas adaptive immune systems to defend themselves from infection by bacteriophages (phages). These RNA-guided nucleases are powerful weapons in the fight against foreign DNA, such as phages and plasmids, as well as a revolutionary gene editing tool. Phages are not passive bystanders in their interactions with CRISPR-Cas systems, however; recent discoveries have described phage genes that inhibit CRISPR-Cas function. More than 20 protein families, previously of unknown function, have been ascribed anti-CRISPR function. Here, we discuss how these CRISPR-Cas inhibitors were discovered and their modes of action were elucidated. We also consider the potential impact of anti-CRISPRs on bacterial and phage evolution. Finally, we speculate about the future of this field.


CRISPR-Cas; Cas9; anti-CRISPR; bacteriophage

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