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). This protein plus Cascade participate in CRISPR interference, the third stage of CRISPR immunity (By similarity). Plasmid targeted by CRISPR locus P1 transform wild-type cells very poorly (PubMed:22767603). Loss of the 8 Cas genes in this locus (cas1, cas2, cas3, cas4, cas5, cas6, cas7 and cas8b) leads to loss of CRISPR interference against plasmid targeted by this CRISPR locus, i.e. plasmid is not destroyed by CRISPR. Disruption of this single gene also leads to loss of CRISPR interference. There are 3 CRISPR RNA loci in this organism and a single cas gene locus. A CRISPR-Cas type I-B system. 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.