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 enzyme processes pre-crRNA into individual crRNA units, but may not actually undergo enzyme turnover, retaining the crRNA product (PubMed:21572442). Generates a 2',3'-cyclic phosphodiester. Probably part of the Cascade ribonucleoprotein complex (Probable). Monomer, retains crRNA after it is processed. Belongs to the CRISPR-associated protein Cas6/Cse3/CasE family. Subtype I-E/Ecoli subfamily.