CRISPR (clustered regularly interspaced short palindromic repeat) is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). Functions as a ssRNA-specific endoribonuclease. Involved in the integration of spacer DNA into the CRISPR cassette. Homodimer, forms a heterotetramer with a Cas1 homodimer. In culture expression is high during mid-log phase (2 hour), then decreases to nearly undetectable levels in late stationary phase (16 hours). During infection of mouse bone marrow-derived macrophages (BMDM) expression is maximal after 1 hour, when the bacteria is expected to be in the phagosome. No effect on expression of bacterial lipoprotein FTN_1103. Bacteria are as virulent in mice as wild-type bacteria. Part of a type II CRISPR-Cas system. Belongs to the CRISPR-associated endoribonuclease Cas2 protein family.