Cas4

Cas4 is an endonuclease found in some CRISPR systems that is used as part of the spacer acquisition stage.

Geobacter sulfurreducens Cas1-Cas2-Cas4 complex bound to double stranded protospacer adjacent motif (PAM) spacer DNA. Cas1 homodimers (blue) bind to each side of the Cas2 homodimer (red) with a Cas4 Fe-S nuclease (cyan) bridging the two. The 3′ end of each DNA strand threads into the Cas4 active site. PDB: 7MI4​

CRISPR-associated protein 4
Pyrobaculum calidifontis Cas4, PDB: 4R5Q​
Identifiers
Symbol	cas4
Pfam	PF01930
InterPro	IPR022765
Available protein structures: Pfam   structures / ECOD   PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Cas4 is required for efficient prespacer processing by forming a Cas4-Cas1-Cas2 complex. ^[1] In this complex, Cas4 cuts double-stranded substrates with long 3'-overhangs through site-specific endonucleolytic cleavage. ^[2] Cas4 closely interacts with the integrase active sites of Cas1, recognizes PAM sequences within the substrate and cleaves precisely upstream of them, ensuring the acquisition of functional spacers. ^{[2] [1]}