Structures of the CRISPR-Cmr complex reveal mode of RNA target positioning

Changing shape to destroy RNA Clustered regularly interspaced short palindromic repeats (CRISPRs) together with CRISPR-associated (Cas) proteins form an adaptive immune system that helps bacteria and archaea defend themselves against invading viruses and plasmids. CRISPR RNAs (crRNAs) target CRISPR-Cas protein complexes to the invaders, bringing about their destruction. Taylor et al. used cryo–electron microscopy to determine the structure of a 12-subunit CRISPR-Cas protein complex with crRNA from Thermus thermophilus , in the presence and absence of single-stranded target RNA. Binding to the target RNA causes a change in shape of the CRISPR-Cas complex that results in target recognition and destruction. Science , this issue p. 581