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 (spacers) and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). The type III-A Csm effector complex binds crRNA and acts as a crRNA-guided RNase, DNase and cyclic oligoadenylate synthase; binding of target RNA cognate to the crRNA is required for all activities (Probable). This CRISPR-Cas system protects bacteria against transformation with plasmids containing DNA homologous to its spacer regions (PubMed:29979631). Processes pre-crRNA into individual crRNA units; accurate cleavage of pre-crRNA depends on a 3' stem-loop and the sequence of the bases in the stem. The mature crRNA is unusual for type III-A systems as it doe snot undergo 3' processing after Cas6 cleavage. Mature crRNA is about 71 nucleotides (nt long) with an 8 nt 5' handle and 28 nt repeat with a 10 nt stem-loop at the 3' end. Ca(2+) and Mn(2+) stimulate processing of pre-crRNA. Pre-crRNA processing is inhibited by EDTA. kcat is 12.156 min(-1) in presence of CaCl(2). Deletion of this gene alone blocks maturation of pre-crRNA (PubMed:29979631). Deletion of the entire CRISPR-Cas locus (cas6 to cas2, Rv2824c to Rv2816c) decreases resistance to plasmids encoding spacer elements about 6-fold (PubMed:29979631). Encoded in a type III-A CRISPR locus. Belongs to the CRISPR-associated protein Cas6/Cse3/CasE family.