Cas9-type HNH domain (IPR033114)

Short name: HNH_CAS9

Overlapping homologous superfamilies


Domain relationships



The CRISPR (clustered regularly interspaced short palindromic repeat)-Cas (CRISPR associated) system is a naturally occuring, adaptative microbial immune system for defense against invading phages and other mobile genetic elements. Type II CRISPR-Cas systems use an RNA-guided DNA endonuclease, Cas9, to generate double strand breaks in invasive DNA during an adaptative bacterial immune response. Cas9 proteins are abundant across the bacterial kingdom, but vary widely in both sequence and size. All known Cas9 enzymes contain an HNH domain that cleaves the DNA strand complementary to the guide RNA sequence (target strand), and a RuvC nuclease domain required for cleaving the noncomplementary strand (non-target strand), yielding double strand DNA breaks (DSBs) [PMID: 24505130, PMID: 24529477].

The Cas9-type HNH nuclease domain contains a two-stranded antiparallel beta sheet flanked by two alpha-helices on each side [PMID: 24505130, PMID: 24529477]. This entry covers the entire Cas9-type HNH domain.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles