CRISPR system Cmr endoribonuclease Cmr4

UniProtKB accession:  Q8U1S9

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UniProtKB description:  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), formerly called psiRNA (prokaryotic silencing) in this organism. Part of the Cmr ribonucleoprotein complex which has divalent cation-dependent endoribonuclease activity specific for ssRNA complementary to the crRNA (target RNA), generating 5' hydroxy- and 3' phosphate or 2'-3' cyclic phosphate termini. This is probably the subunit that cleaves the target RNA (PubMed:25280103). Cmr complex does not cleave ssDNA complementary to the crRNA. Cleavage of target RNA is guided by the crRNA; substrate cleavage occurs a fixed distance (14 nt) from the 3' end of the crRNA. In vitro reconstitution shows Cmr1-2 and Cmr5 are not absolutely necessary for target cleavage (PubMed:19945378).