Component of the MRE11-RAD50-NBN (MRN complex) which plays a critical role in the cellular response to DNA damage and the maintenance of chromosome integrity. The complex is involved in double-strand break (DSB) repair, DNA recombination, maintenance of telomere integrity, cell cycle checkpoint control and meiosis. The complex possesses single-strand endonuclease activity and double-strand-specific 3'-5' exonuclease activity (By similarity). Component of the MRN complex composed of two heterodimers rad50/mre11 associated with a single nbn. The EEXXXDDL motif at the C-terminus is required for the interaction with atm and its recruitment to sites of DNA damage and promote the phosphorylation of atm substrates, leading to the events of DNA damage response.