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- Title
The ndh-binding protein (Nbp) regulates the ndh gene of Escherichia coli in response to growth phase and is identical to Fis.
- Authors
Green, J.; Anjum, M. F.; Guest, J. R.
- Abstract
The <em>ndh</em> gene that encodes the non-proton-translocating NADH dehydrogenase II of <em>Escherichia coli</em> is anaerobically repressed by FNR. However, in the absence of FNR, <em>ndh</em> expression is enhanced by anaerobic growth in media containing amino acids. Two potential regulatory proteins that may be associated with this activation have previously been detected, Arr (amino acid response regulator) and Nbp (<em>ndh</em>-binding protein). Studies with the heat-stable Nbp have now shown that it is present in <em>E. coli</em> grown both aerobically and anaerobically in rich and minimal media, indicating that it is not specifically associated with the anaerobic enhancement of <em>ndh</em> expression. The Nbp activity of aerobic cultures was maximal during exponential growth phase (when <em>ndh</em> promoter activity is minimal) but fell rapidly as cultures entered stationary phase and <em>ndh</em> expression increased. Protein purification and mutant studies have further shown that Nbp is identical to the Fis protein (f̱actor for i̱nversion s̱timulation). Three major and two minor Nbp (Fis)-binding sites have been identified in the <em>ndh</em> promoter by gel retardation and DNase I footprinting. The major sites are centred at -123, -72 and +51, in decreasing order of binding affinity. At low concentrations, Nbp (Fis) increased transcription from the <em>ndh</em> promoter by up to 25%, whereas at higher concentrations it prevented RNA polymerase (RNAP) binding and open complex formation. Consequently, Nbp (Fis) can both activate and repress transcription from the <em>ndh</em> promoter. The results suggest that Nbp (Fis) serves to ensure that the energetically efficient proton-translocating NADH dehydrogenase I is used in preference to the nonproton translocating NADH dehydrogenase II during periods of rapid growth, by repressing expression of the <em>ndh</em> gene.
- Subjects
ESCHERICHIA coli; NAD(P)H dehydrogenases; CARRIER proteins; AMINO acids; BACTERIAL growth; RNA polymerases; GENE expression
- Publication
Molecular Microbiology, 1996, Vol 20, Issue 5, p1043
- ISSN
0950-382X
- Publication type
Article
- DOI
10.1111/j.1365-2958.1996.tb02545.x