PreprintCited by 4CRISPR and Genetic EngineeringRNA regulation and diseaseBacterial Genetics and Biotechnology

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Structural basis for a dual-function type II-B CRISPR-Cas9

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Hibshman, Grace N., Taylor, David W.·2024·Nucleic Acids Research

Preprint — published as 10.1093/nar/gkaf585 · Paper page

Abstract

Cas9 from Streptococcus pyogenes (SpCas9) revolutionized genome editing by enabling programmable DNA cleavage guided by an RNA. However, SpCas9 tolerates mismatches in the DNA-RNA duplex, which can lead to deleterious off-target editing. Here, we reveal that Cas9 from Francisella novicida (FnCas9) possesses a unique structural feature—the REC3 clamp—that underlies its intrinsic high-fidelity DNA targeting. Through kinetic and structural analyses, we show that the REC3 clamp forms critical contacts with the PAM-distal region of the R-loop, thereby imposing a novel checkpoint during enzyme activation. Notably, F. novicida encodes a non-canonical small CRISPR-associated RNA (scaRNA) that enables FnCas9 to repress an endogenous bacterial lipoprotein gene, subverting host immune detection. Structures of FnCas9 with scaRNA illustrate how partial R-loop complementarity hinders REC3 clamp docking and prevents cleavage in favor of transcriptional repression. The REC3 clamp is conserved in type II-B CRISPR-Cas9 systems, pointing to a potential path for engineering precise genome editors or developing novel antibacterial strategies. These findings reveal the dual mechanisms of high specificity and virulence by FnCas9, with broad implications for biotechnology and therapeutic development. Graphical Abstract:

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Metadata

Authors
Hibshman, G. N., & Taylor, D. W.
Affiliations
The University of Texas at Austin (US)
Corresponding author
Taylor, David W.
Venue
Nucleic Acids Research
Publisher
openRxiv
Published
2024-10-24
Volume
53
Issue
12
ISSN
0305-1048 (ISSN-L)
OpenAlex
W4412034271
Cited by
4
References
1
Citations by year
2026: 2 · 2025: 2
FWCI
1.20
Type
journal article
Language
en
Open access
Locations
  • Nucleic Acids Research (publishedVersion, cc-by)
  • bioRxiv (Cold Spring Harbor Laboratory) (acceptedVersion)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • PubMed Central (submittedVersion)
Funders
  • Welch Foundation (F-1938)
  • National Institutes of Health (F-1938)
  • National Institute of General Medical Sciences (R35GM138348)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › CRISPR and Genetic Engineering
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › RNA regulation and disease
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Bacterial Genetics and Biotechnology
Keywords
Francisella novicida, off-target editing, R-loops, transcriptional repression, lipoprotein gene, host immune evasion, antibacterial strategies, genome editing specificity

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