This family of bacterial proteins includes a sodium-translocating NADH-ubiquinone oxidoreductase (i.e. a respiration linked sodium pump). In Vibrio cholerae, it negatively regulates the expression of virulence factors through inhibiting (by an unknown mechanism) the transcription of the transcriptional activator ToxT. The family also includes proteins involved in nitrogen fixation, RnfD and RnfE. The similarity of these proteins to NADH-ubiquinone oxidoreductases was previously noted.