A two-step target capture process—specific but low-affinity PAM binding followed by rapid DNA unwinding—underpins efficient CRISPR-Cas9 editing. Shi et al. show that PAM-relaxed Cas9 variants like SpRY become kinetically trapped between these steps, reducing editing efficiency. These insights provide new principles for engineering improved RNA-guided genome editors.

Microbial and viral co-evolution has created immunity mechanisms involving oligonucleotide signaling that share mechanistic features with human anti-viral systems. In these pathways, including CBASS a...