TRANSCRIPTIONAL REGULATION OF THE PROTON-TRANSLOCATING NADH DEHYDROGENASE GENES (NUOA-N) OF ESCHERICHIA-COLI BY ELECTRON-ACCEPTORS, ELECTRON-DONORS AND GENE REGULATORS

The promoter region and transcriptional regulation of the nuoA-N gene locus encoding the proton-translocating NADH:quinone oxidoreductase was analysed. A 560 bp intergenic region upstream of the nuo locus was followed by a gene (designated IrhA for LysR homologue A) coding for a gene regulator similar to those of the LysR family. Disruption of IrhA did not affect growth (respiratory or non-respiratory) or expression of nuo significantly. Transcriptional regulation of nuo by electron accepters, electron donors and the transcriptional regulators ArcA, END, NarL and NarP, and by IHF (integration host factor) was studied with protein and operon fusions containing the promoter region up to base pair -277 ('nuo(277)') or up to base pair -899 ('nuo(899)'). The expression of the nuo(277)-lacZ fusions was subject to ArcA-mediated anaerobic repression and NarL(+ nitrate)-mediated anaerobic activation. FNR and ii-if acted as weak repressors under anaerobic conditions. Expression of nuo(899)-lacZ was stimulated during anaerobic fumarate respiration and aerobically by C-4 dicarboxylates. Therefore, expression of nuo is regulated by O-2 and nitrate via ArcA, NarL, FNR and IHF at sites within the -277 region, and by other factors including C-4 dicarboxylates at a site between -277 and -899. A physiological role for the transcriptional stimulation by O-2 and nitrate is suggested.