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 and Cascade participate in CRISPR interference, the third stage of CRISPR immunity (Potential). Absolutely required for crRNA production or stability. The Csy ribonucleoprotein complex binds target ssDNA with high affinity but target dsDNA with much lower affinity. Interacts directly with Csy1; part of the Csy ribonucleoprotein complex with a probable stoichiometry of Csy1(1),Csy2(1),Csy3(6),Cas6/Csy4(1)-crRNA(1). A Csy3(6),Cas6/Csy4(1)-crRNA(1) subcomplex is also formed. Mutants lose phage DMS3 infection-dependent inhibition of biofilm formation while there is normal biofilm formation in the absence of phage infection. Loss of 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, and the flanking CRISPR loci), indicating this CRISPR is not involved in phage resistance. In this bacteria, Y.pestis-subtype CRISPRs do not confer resistance to phage DMS3 or MP22, but instead are required for DMS3 infection-dependent inhibition of biofilm formation and possibly motility. Belongs to the CRISPR-associated Csy2 family.