RAD9 Homolog (RAD9)

RAD9 is highly similar to Schizosaccharomyces pombe rad9, a cell cycle checkpoint protein required for cell cycle arrest and DNA damage repair in response to DNA damage. This protein is found to possess 3' to 5' exonuclease activity, which may contribute to its role in sensing and repairing DNA damage. It forms a checkpoint protein complex with RAD1 and HUS1. This complex is recruited by checkpoint protein RAD17 to the sites of DNA damage, which is thought to be important for triggering the checkpoint-signaling cascade. In vivo, the human RAD9 protein was phosphorylated in response to DNA damage, suggesting that it participates in a DNA damage-inducible signaling pathway. Immunoprecipitation studies demonstrated that the fully modified form of RAD9 interacts selectively with RAD1 and HUS1 in a stable complex.