Component of the MRE11-RAD50-NBN complex (MRN complex) which plays a critical role in the cellular response to DNA damage and the maintenance of chromosome integrity. The complex may be involved in double-strand break (DSB) repair, DNA recombination, maintenance of telomere integrity, and cell cycle checkpoint control. Functions also in the very early stages of meiosis. Component of the MRN complex composed of two heterodimers RAD50/MRE11 associated with a single NBN (By similarity). Interacts with MRE11 (By similarity). The FHA and BRCT domains are likely to have a crucial role for both binding to histone H2AFX and for relocalization of MRE11/RAD50 complex to the vicinity of DNA damage.