CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) and associated Cas proteins comprise a system for heritable host defense by prokaryotic cells against phage and other foreign DNA; Very large protein containing McrA/HNH-nuclease related domain and a RuvC-like nuclease domain; signature gene for type II
Jiyao W et al.(2023). "The conserved domain database in 2023.",