Mre11-Rad50-Nbs1 (MRN) is a complex of proteins involved in DNA damage repair in mammals. Nbs1 is referred to as Nibrin. ^[1] This complex recognizes DNA damage and rapidly relocates to DSB sites and forms nuclear foci. Its activity includes end-processing of both physiological and mutagenic DNA double strand breaks (DSBs).^[2]. It appears that as part of its end-processing of DSBs, short single-strand oligonucleotides are produced, which induce activation of Ataxia Telangiectasia-Mutated (ATM) (PMID 18596698), ultimately leading to activation of the DNA damage checkpoint.

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