Part of the Rad50/Mre11 complex, which is involved in the early steps of DNA double-strand break (DSB) repair. The complex may facilitate opening of the processed DNA ends to aid in the recruitment of HerA and NurA. Mre11 binds to DSB ends and has both double-stranded 3'-5' exonuclease activity and single-stranded endonuclease activity. Binds 2 manganese ions per subunit. Nuclease activity is regulated by Rad50. Homodimer. Forms a heterotetramer composed of two Mre11 subunits and two Rad50 subunits. Belongs to the MRE11/RAD32 family.