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 probably processes pre-crRNA into individual crRNA units, and also plays a role in generation or stability of the CRISPR leader-repeat transcript. Cleaves an endogenous (non-invading) RNA; cuts a specific site within a sequence nearly identical to the cognate CRISPR repeat sequence in the 5' UTR of the transcript of provirus gene phiH, found in provirus 1. This digestion might be responsible for inhibiting (defective) provirus 1 excision. Does not produce mature length crRNA; precursor is non-specifically degraded. No accumulation of the CRISPR leader-repeat transcript. Allows excision of defective provirus 1 from its chromosomal locus (detected as restoration of the attachment site attA). There are 6 CRISPR RNA loci in this organism and a single cas gene locus. A CRISPR-Cas type I-B system. Belongs to the CRISPR-associated protein Cas6/Cse3/CasE family.