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). Plasmid targeted by CRISPR locus P1 transform wild-type cells very poorly. This protein helps process or stabilize pre-crRNA into individual crRNA units, in vivo Cas5 and Cas6 are also required for optimal crRNA processing and/or stability