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Mol Cell. 2019 Jul 11;75(1):90-101.e5. doi: 10.1016/j.molcel.2019.04.020. Epub 2019 May 9.

Structure of the DNA-Bound Spacer Capture Complex of a Type II CRISPR-Cas System.

Author information

1
Section of Structural Biology, Department of Medicine, Imperial College London, London SW7 2AZ, UK.
2
Institute of Biotechnology, Vilnius University, Vilnius, Lithuania.
3
Institute of Biotechnology, Vilnius University, Vilnius, Lithuania. Electronic address: siksnys@ibt.lt.
4
Section of Structural Biology, Department of Medicine, Imperial College London, London SW7 2AZ, UK. Electronic address: d.wigley@imperial.ac.uk.

Abstract

CRISPR and associated Cas proteins function as an adaptive immune system in prokaryotes to combat bacteriophage infection. During the immunization step, new spacers are acquired by the CRISPR machinery, but the molecular mechanism of spacer capture remains enigmatic. We show that the Cas9, Cas1, Cas2, and Csn2 proteins of a Streptococcus thermophilus type II-A CRISPR-Cas system form a complex and provide cryoelectron microscopy (cryo-EM) structures of three different assemblies. The predominant form, with the stoichiometry Cas18-Cas24-Csn28, referred to as monomer, contains ∼30 bp duplex DNA bound along a central channel. A minor species, termed a dimer, comprises two monomers that sandwich a further eight Cas1 and four Cas2 subunits and contains two DNA ∼30-bp duplexes within the channel. A filamentous form also comprises Cas18-Cas24-Csn28 units (typically 2-6) but with a different Cas1-Cas2 interface between them and a continuous DNA duplex running along a central channel.

PMID:
31080012
PMCID:
PMC6620040
DOI:
10.1016/j.molcel.2019.04.020
[Indexed for MEDLINE]
Free PMC Article

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