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Description

CRISPR-associated endonuclease Cas9 (UniProt: J7RUA5, also known as SaCas9, Cas9) is encoded by the Cas9 gene in Streptococcus aureus. Cas9 belongs to subtype II-A subfamily with one HNH Cas9-type domain. 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 spacers, sequences complementary to antecedent mobile elements, and target invading nucleic acids. Cas9 has a bi-lobed architecture with a recognition lobe (residues 41-425) and a discontinuous nuclease lobe (NUC, residues 1-40 and 453-1053), the crRNA-target DNA lies in a channel between the 2 lobes. The NUC lobe has 2 endonuclease domains. The discontinuous RuvC-like domain in NUC cleaves the target DNA non-complementary to crRNA while the HNH nuclease domain cleaves the target DNA complementary to crRNA. Cas9 serves as a RNA-guided DNA endonuclease that cleaves double-stranded DNA targets with a protospacer adjacent motif (PAM) and complementarity to the guide RNA. The homologous region of the Streptococcus pyogenes is not closely related in amino acid sequence in S. aureus, hence this antibody does not recognize that protein.