MRE11A gene encodes a nuclear protein which plays a central role in double-strand break (DSB) repair, DNA homologous recombination, maintenance of telomere integrity and meiosis, as a part of the MRN complex. By itself, the protein has 3' to 5' exonuclease activity and endonuclease activity. The protein forms a complex with the RAD50 homolog; this complex is required for nonhomologous joining of DNA ends and possesses increased single-stranded DNA endonuclease and 3' to 5' exonuclease activities. In conjunction with a DNA ligase, this protein promotes the joining of noncomplementary ends in vitro using short homologies near the ends of the DNA fragments.

Mutations in MRE11A gene are responsible for ataxia telangiectasia-like disorder (ATLD). Mutations in this gene are also thought to be a cause of breast cancer.