Part of the Rad50/Mre11 complex, which is involved in the early steps of DNA double-strand break (DSB) repair. Rad50 controls the balance between DNA end bridging and DNA resection via ATP-dependent structural rearrangements of the Rad50/Mre11 complex (By similarity). In polyploid organisms, the Rad50/Mre11 complex appears to restrain the repair of double-strand breaks by homologous recombination, allowing another pathway to act as the primary mode of repair (PubMed:19593371). Binds 1 zinc ion per homodimer. Homodimer. Forms a heterotetramer composed of two Mre11 subunits and two Rad50 subunits. The two conserved Cys that bind zinc constitute the zinc-hook, which separates the large intramolecular coiled coil regions. The 2 Cys residues coordinate one molecule of zinc with the help of the 2 Cys residues of the zinc-hook of another Rad50 molecule, thereby forming a V-shaped homodimer. Mutants are more resistant to DNA damage, but recover more slowly than the wild-type. Belongs to the SMC family. RAD50 subfamily.