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Mol Cell. 2016 Sep 1;63(5):840-51. doi: 10.1016/j.molcel.2016.07.027.

DNA Targeting by a Minimal CRISPR RNA-Guided Cascade.

Author information

1
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
2
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address: dtaylor@utexas.edu.
3
Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA.
4
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
5
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA 94720, USA; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA. Electronic address: doudna@berkeley.edu.

Abstract

Bacteria employ surveillance complexes guided by CRISPR (clustered, regularly interspaced, short palindromic repeats) RNAs (crRNAs) to target foreign nucleic acids for destruction. Although most type I and type III CRISPR systems require four or more distinct proteins to form multi-subunit surveillance complexes, the type I-C systems use just three proteins to achieve crRNA maturation and double-stranded DNA target recognition. We show that each protein plays multiple functional and structural roles: Cas5c cleaves pre-crRNAs and recruits Cas7 to position the RNA guide for DNA binding and unwinding by Cas8c. Cryoelectron microscopy reconstructions of free and DNA-bound forms of the Cascade/I-C surveillance complex reveal conformational changes that enable R-loop formation with distinct positioning of each DNA strand. This streamlined type I-C system explains how CRISPR pathways can evolve compact structures that retain full functionality as RNA-guided DNA capture platforms.

PMID:
27588603
PMCID:
PMC5111854
[Available on 2017-03-01]
DOI:
10.1016/j.molcel.2016.07.027
[Indexed for MEDLINE]
Free PMC Article

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