HUS1 is a component of an evolutionarily conserved， genotoxin-activated checkpoint complex. HUS1 protein connects with Rad9 and Rad1 to form the 9-1-1（RAD9-RAD1-HUS1） complex， that confines to DNA lesions and promotes DNA damage signaling and repair or apoptosis， cell cycle arrest. The trimeric complex is structurally similar to the proliferating cell nuclear antigen （PCNA） sliding clamp and interacts with Rad17 as a clamp-clamp loader pair during the DNA damage response.
