Abstract
In this issue of Molecular Cell, Rotheneder et al.(1) elucidate the eukaroytic Mre11-Rad50-Nbs1 (MRN) complex quaternary architecture, which together with cryo-EM structures of bacterial Mre11-Rad50-DNA complexes,(2) resolves the basis for MRN assembly and its broad nuclease specificity regulating DNA double-strand break repair.