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CRISPR-Cas12a exploits R-loop asymmetry to form double-strand breaks.

eLife | 2020

Type V CRISPR-Cas interference proteins use a single RuvC active site to make RNA-guided breaks in double-stranded DNA substrates, an activity essential for both bacterial immunity and genome editing. The best-studied of these enzymes, Cas12a, initiates DNA cutting by forming a 20-nucleotide R-loop in which the guide RNA displaces one strand of a double-helical DNA substrate, positioning the DNase active site for first-strand cleavage. However, crystal structures and biochemical data have not explained how the second strand is cut to complete the double-strand break. Here, we detect intrinsic instability in DNA flanking the RNA-3' side of R-loops, which Cas12a can exploit to expose second-strand DNA for cutting. Interestingly, DNA flanking the RNA-5' side of R-loops is not intrinsically unstable. This asymmetry in R-loop structure may explain the uniformity of guide RNA architecture and the single-active-site cleavage mechanism that are fundamental features of all type V CRISPR-Cas systems.

Pubmed ID: 32519675 RIS Download

Associated grants

  • Agency: NIGMS NIH HHS, United States
    Id: T32 GM008295
  • Agency: Howard Hughes Medical Institute, United States
  • Agency: National Science Foundation, International
    Id: MCB-1817593

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