rAcrIIA1

A phage-encoded small RNA that mimics chimeric guide to inhibit CRISPR-Cas9

CRISPR Cas9 relies on a dual crRNA-tracrRNA guide, yet whether RNA based anti CRISPRs exist for this system has remained unknown. Here we identify a phage encoded small non coding RNA, rAcrIIA1, that adopts an unexpected chimeric crRNA-tracrRNA architecture, faithfully recapitulating the entire single guide RNA (sgRNA) of Cas9. Cryo EM structures of the Cas9-rAcrIIA1 binary complex and the Cas9-rAcrIIA1-DNA ternary complex reveal that rAcrIIA1 engages Cas9 nearly identically to the native...