This family consists of several bacterial dinitrogenase reductase ADP-ribosyltransferase (DRAT) proteins. Members of this family seem to be specific to Rhodospirillum, Rhodobacter and Azospirillum species. Dinitrogenase reductase ADP-ribosyl transferase (DRAT) carries out the transfer of the ADP-ribose from NAD to the Arg-101 residue of one subunit of the dinitrogenase reductase homodimer, resulting in inactivation of that enzyme. Dinitrogenase reductase-activating glycohydrolase (DRAG) removes the ADP-ribose group attached to dinitrogenase reductase, thus restoring nitrogenase activity. The DRAT-DRAG system negatively regulates nitrogenase activity in response to exogenous NH4+ or energy limitation in the form of a shift to darkness or to anaerobic conditions.