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 spacers, sequences complementary to antecedent mobile elements, and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). This protein is a sequence-specific endonuclease that cleaves pre-crRNA into mature crRNA, possibly by an intramolecular attack of the 2'-hydroxyl group of G26 on the scissile phosphodiester, cutting the precursor 3' to G26 residue yielding 5'-hydroxyl and 2' and/or 3' ends lacking a hydroxyl group (perhaps a 2'/3' cyclic phosphodiester). Requires between 4 and 8 nt downstream of the cleavage site for both binding and cleavage of pre-crRNA. Substitution with dG at this position abolishes cleavage but not RNA binding. Does not cleave pre-crRNA associated with the M.succiniciproducens strain MBEL55E Cas5 protein (AC Q65TW5) CRISPR locus. Does not require a metal cofactor. Belongs to the CRISPR-associated protein Cas5 family. Subtype I-C/Dvulg subfamily.