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). Cas3 plus Cascade participate in CRISPR interference, the third stage of CRISPR immunity (Potential). In this bacteria Y.pestis-subtype CRISPRs do not confer resistance to phage DSM3 or MP22, but instead are required for DMS3-dependent inhibition of biofilm formation and possibly motility. Interacts with Cas1. Infection with phage DSM3 inhibits biofilm formation; disrupting this gene restores biofilm formation upon infection with DMS3 infection. Normal biofilm formation in the absence of phage infection. Decreased production of crRNA in the presence or absence of phage. Disruption of the entire Y.pestis-subtype CRISPR region disrupts crRNA production but does not alter phage resistance (possibly OLNs PA14_33350 to PA14_33310, plus the flanking CRISPR loci), indicating this CRISPR is not involved in phage resistance. In the N-terminal section; belongs to the CRISPR-associated nuclease Cas3-HD family. In the central section; belongs to the CRISPR-associated helicase Cas3 family.