Involved in DNA double-strand break repair (DSBR). Possesses single-strand endonuclease activity and double-strand-specific 3'-5' exonuclease activity. Also involved in meiotic DSB processing. Binds 2 manganese ions per subunit. Component of the MRN complex composed of two heterodimers RAD50/MRE11 associated with a single NBN (By similarity). Interacts with NBS1. Belongs to the MRE11/RAD32 family. Truncated N-terminus.