CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a widespread family of prokaryotic direct repeats with spacers of unique sequence between consecutive repeats. This entry, typified by YPO2465 of Yersinia pestis, is a CRISPR-associated (Cas) entry strictly associated with the Ypest subtype of CRISPR/Cas locus. It is designated Csy1, for CRISPR/Cas Subtype Ypest protein 1.