DNA Targeting by a Minimal CRISPR RNA-Guided Cascade

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

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Binding Sites
  • CRISPR-Cas Systems*
  • Cloning, Molecular
  • Cryoelectron Microscopy
  • DNA / chemistry
  • DNA / genetics*
  • DNA / metabolism
  • Desulfovibrio vulgaris / genetics*
  • Desulfovibrio vulgaris / metabolism
  • Endonucleases / chemistry
  • Endonucleases / genetics*
  • Endonucleases / metabolism
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Gene Editing
  • Gene Expression
  • Kinetics
  • Models, Molecular
  • Nucleic Acid Conformation
  • Operon
  • Protein Binding
  • Protein Conformation, alpha-Helical
  • Protein Interaction Domains and Motifs
  • RNA, Bacterial / chemistry
  • RNA, Bacterial / genetics*
  • RNA, Bacterial / metabolism
  • RNA, Guide / chemistry
  • RNA, Guide / genetics*
  • RNA, Guide / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Substrate Specificity

Substances

  • Bacterial Proteins
  • RNA, Bacterial
  • RNA, Guide
  • Recombinant Proteins
  • DNA
  • Endonucleases