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