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 [1].

1: Effect of P(II) and its homolog GlnK on reversible ADP-ribosylation of dinitrogenase reductase by heterologous expression of the Rhodospirillum rubrum dinitrogenase reductase ADP-ribosyl transferase-dinitrogenase reductase-activating glycohydrolase regula Zhang Y, Pohlmann EL, Halbleib CM, Ludden PW, Roberts GP; J Bacteriol 2001;183:1610-1620. PMID:11160092