CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a widespread family of prokaryotic direct repeats with spacers of unique sequence between consecutive repeats. This protein family, typified by YPO2462 of Yersinia pestis, is a CRISPR-associated (Cas) family strictly associated with the Ypest subtype of CRISPR/Cas locus. It is designated Csy4, for CRISPR/Cas Subtype Ypest protein 4.