Nijmegen breakage syndrome protein 1 (NBS1) is a component of the MRE11/RAD50/NBN (MRN) comple, Xenopus/Amphibian,, which plays a critical role in the cellular response to DNA damage and the maintenance of chromosome integrity. The comple, Xenopus/Amphibian, is involved in double-strand break (DSB) repair, DNA recombination,Mouse,aintenance of telomere integrity, cell cycle checkpoint control and meiosis. NBS1 modulates the DNA damage signal sensing by recruiting PI3/PI4-kinase family members ATM, ATR, and probably DNA-PKcs to the DNA damage sites and activating their functions. Defects in NBS1 are the cause of Nijmegen breakage syndrome, cancer predisposition, and anemia.