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Science. 2015 May 1;348(6234):581-5. doi: 10.1126/science.aaa4535. Epub 2015 Apr 2.

Structural biology. Structures of the CRISPR-Cmr complex reveal mode of RNA target positioning.

Author information

1
Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA. California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA.
2
Laboratory of Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, 6703 HB Wageningen, Netherlands.
3
Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.
4
RIKEN SPring-8 Center, Hyogo 679-5148, Japan. RIKEN Structural Biology Laboratory, Kanagawa 230-0045, Japan.
5
Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA. California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA. Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA. Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. doudna@berkeley.edu enogales@lbl.gov.
6
Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA. California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA. Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA. Department of Chemistry, University of California, Berkeley, CA 94720, USA. Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. doudna@berkeley.edu enogales@lbl.gov.

Abstract

Adaptive immunity in bacteria involves RNA-guided surveillance complexes that use CRISPR (clustered regularly interspaced short palindromic repeats)-associated (Cas) proteins together with CRISPR RNAs (crRNAs) to target invasive nucleic acids for degradation. Whereas type I and type II CRISPR-Cas surveillance complexes target double-stranded DNA, type III complexes target single-stranded RNA. Near-atomic resolution cryo-electron microscopy reconstructions of native type III Cmr (CRISPR RAMP module) complexes in the absence and presence of target RNA reveal a helical protein arrangement that positions the crRNA for substrate binding. Thumblike β hairpins intercalate between segments of duplexed crRNA:target RNA to facilitate cleavage of the target at 6-nucleotide intervals. The Cmr complex is architecturally similar to the type I CRISPR-Cascade complex, suggesting divergent evolution of these immune systems from a common ancestor.

PMID:
25837515
PMCID:
PMC4582657
DOI:
10.1126/science.aaa4535
[Indexed for MEDLINE]
Free PMC Article

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