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

A phage-encoded small RNA, rAcrIIA1, mimics sgRNA to inhibit CRISPR-Cas9 and can be reprogrammed for sequence-specific DNA cleavage.

• Why it matters: Understanding RNA-based anti-CRISPRs is crucial for developing new tools to control CRISPR-Cas9 activity and improve genome editing precision.
• What they did: Researchers identified rAcrIIA1, a small non-coding RNA with a chimeric crRNA-tracrRNA structure, and used cryo-EM to show it engages Cas9 similarly to native sgRNA, blocking DNA interference.
• The result: rAcrIIA1 not only inhibits Cas9 via sgRNA mimicry but can be reprogrammed with variable guides to direct efficient, sequence-specific DNA cleavage and enhance trans-cleavage activity, enabling versatile genome editing and diagnostics.