151. CRISPR-Cas12a exploits R-loop asymmetry to form double-strand breaks
- Author
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Cofsky, Joshua C, Karandur, Deepti, Huang, Carolyn J, Witte, Isaac P, Kuriyan, John, and Doudna, Jennifer A
- Subjects
Biochemistry and Cell Biology ,Bioinformatics and Computational Biology ,Biological Sciences ,Genetics ,Prevention ,1.1 Normal biological development and functioning ,Underpinning research ,Generic health relevance ,Bacterial Proteins ,CRISPR-Associated Proteins ,CRISPR-Cas Systems ,DNA ,DNA Breaks ,Double-Stranded ,Endodeoxyribonucleases ,Escherichia coli ,Gene Editing ,R-Loop Structures ,RNA ,Guide ,Kinetoplastida ,CRISPR ,E. coli ,R-loop ,RNA ,biochemistry ,chemical biology ,deoxyribonuclease ,genome editing ,Biological sciences ,Biomedical and clinical sciences ,Health sciences - Abstract
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.
- Published
- 2020