Structure and activity of the RNA-targeting Type III-B CRISPR-Cas complex of Thermus thermophilus

Mol Cell. 2013 Oct 10;52(1):135-145. doi: 10.1016/j.molcel.2013.09.013.

Abstract

The CRISPR-Cas system is a prokaryotic host defense system against genetic elements. The Type III-B CRISPR-Cas system of the bacterium Thermus thermophilus, the TtCmr complex, is composed of six different protein subunits (Cmr1-6) and one crRNA with a stoichiometry of Cmr112131445361:crRNA1. The TtCmr complex copurifies with crRNA species of 40 and 46 nt, originating from a distinct subset of CRISPR loci and spacers. The TtCmr complex cleaves the target RNA at multiple sites with 6 nt intervals via a 5' ruler mechanism. Electron microscopy revealed that the structure of TtCmr resembles a "sea worm" and is composed of a Cmr2-3 heterodimer "tail," a helical backbone of Cmr4 subunits capped by Cmr5 subunits, and a curled "head" containing Cmr1 and Cmr6. Despite having a backbone of only four Cmr4 subunits and being both longer and narrower, the overall architecture of TtCmr resembles that of Type I Cascade complexes.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • CRISPR-Associated Proteins / chemistry
  • CRISPR-Associated Proteins / genetics
  • CRISPR-Associated Proteins / metabolism*
  • Clustered Regularly Interspaced Short Palindromic Repeats
  • High-Throughput Nucleotide Sequencing
  • Microscopy, Electron
  • Models, Molecular
  • Protein Conformation
  • Protein Subunits
  • RNA, Bacterial / chemistry
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism*
  • Ribonucleases / chemistry
  • Ribonucleases / genetics
  • Ribonucleases / metabolism*
  • Sequence Analysis, RNA
  • Spectrometry, Mass, Electrospray Ionization
  • Structure-Activity Relationship
  • Thermus thermophilus / genetics
  • Thermus thermophilus / metabolism*

Substances

  • Bacterial Proteins
  • CRISPR-Associated Proteins
  • Protein Subunits
  • RNA, Bacterial
  • Ribonucleases