Human Dmc1 protein binds DNA as an octameric ring

The bacterial RecA protein has been the most intensively studied enzyme in homologons genetic recombination. The core of RecA is structurally homologo us to that of the F1-ATPase and helicases. Like the FI-ATPase and ring heli cases, RecA forms a hexameric ring. The human Dmc1 (hDmc1) protein, a meios is-specific recombinase, is homologous to RecA, We show that hDmc1 forms oc tameric rings. Unlike RecA and Rad51, however, hDmc1 protein does not form helical filaments. The hDmc1 ring binds DNA in the central channel, as do t he ring helicases,which is likely to represent the active form of the prote in. These observations indicate that the conservation of the RecA-like ring structure extends from bacteria to humans, and that some RecA homologs may form both rings and filaments, whereas others may function only as rings.