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

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

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Clustered Regularly Interspaced Short Palindromic Repeats*
  • Cryoelectron Microscopy
  • Multiprotein Complexes / chemistry*
  • Multiprotein Complexes / ultrastructure
  • RNA / chemistry*
  • RNA / ultrastructure
  • RNA Cleavage*
  • Thermus thermophilus / immunology*

Substances

  • Multiprotein Complexes
  • RNA