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 (By similarity). 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. This protein is about 60 residues too short at the N-terminus compared to its close orthologs.