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Curr Opin Microbiol. 2017 Jun;37:67-78. doi: 10.1016/j.mib.2017.05.008. Epub 2017 Jun 9.

Diversity, classification and evolution of CRISPR-Cas systems.

Author information

1
National Center for Biotechnology Information, National Library of Medicine, Bethesda, MD 20894, USA. Electronic address: koonin@ncbi.nlm.nih.gov.
2
National Center for Biotechnology Information, National Library of Medicine, Bethesda, MD 20894, USA.
3
Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; McGovern Institute for Brain Research at MIT, Cambridge, MA 02139, USA; Departments of Brain and Cognitive Science and Biological Engineering, Cambridge, MA 02139, USA.

Abstract

The bacterial and archaeal CRISPR-Cas systems of adaptive immunity show remarkable diversity of protein composition, effector complex structure, genome locus architecture and mechanisms of adaptation, pre-CRISPR (cr)RNA processing and interference. The CRISPR-Cas systems belong to two classes, with multi-subunit effector complexes in Class 1 and single-protein effector modules in Class 2. Concerted genomic and experimental efforts on comprehensive characterization of Class 2 CRISPR-Cas systems led to the identification of two new types and several subtypes. The newly characterized type VI systems are the first among the CRISPR-Cas variants to exclusively target RNA. Unexpectedly, in some of the class 2 systems, the effector protein is additionally responsible for the pre-crRNA processing. Comparative analysis of the effector complexes indicates that Class 2 systems evolved from mobile genetic elements on multiple, independent occasions.

PMID:
28605718
PMCID:
PMC5776717
DOI:
10.1016/j.mib.2017.05.008
[Indexed for MEDLINE]
Free PMC Article

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