A guide RNA repeat checkpoint steers CRISPR-Cas9 catalysis

A widely adopted CRISPR-Cas9 modification is fusion of the naturally occurring two-component dual guide RNA (dgRNA) to create an artificial single guide RNA (sgRNA). However, mechanistic and functional differences between dgRNA and sgRNA have not been systematically explored. By investigating the activity of these two guide architectures, we discover a guide RNA repeat checkpoint (GRC) that senses the structure and dynamics of the guide repeat region. The GRC coordinates with other checkpoint mechanisms known to recognize spacer-target R-loop fidelity, together licensing target cleavage. Based on these principles, dgRNA and sgRNA properties could be combined into guide repeat-truncated sgRNAs (grtRNAs) and paired with high-fidelity Cas9 variants to further reduce off target editing. A mechanism that helps govern Cas9 catalysis via guide RNA structure sensing and communicates with other checkpoints offers a previously unappreciated path for understanding and further improving gene editing outcomes.