title: Regulation of the Escherichia coli ydhY-T operon in the presence of alternative electron acceptors.
abstract: The Escherichia coli K-12 ydhY-T operon, coding for a predicted oxidoreductase complex, is activated under anaerobic conditions and repressed in the presence of nitrate or nitrite. Anaerobic activation is mediated by the transcription factor FNR, and nitrate/nitrite repression is mediated by NarXL and NarQP. In vitro transcription reactions revealed that the DNA upstream of ydhY-T contains sufficient information for RNA polymerase alone to initiate transcription from five locations. FNR severely inhibited synthesis of two of these transcripts (located upstream of, and within, the FNR binding site) and activated the FNR-dependent promoter previously identified in vivo. Enhanced expression of ydhY-T in an hns mutant was consistent with the location of ydhY-T within a promoter island and the FNR-independent transcription observed in vitro. FNR-dependent transcription in vitro was decreased in the presence of NarL~P. DNaseI footprinting indicated that FNR and NarL~P simultaneously bound at the ydhY-T promoter region and that NarL~P-mediated repression was due to occupation of the 7-2-7 site located downstream of the FNR-dependent promoter. Expression of ydhY-T during the anaerobic growth cycle was repressed when nitrate was present but less so in the presence of nitrite. In vivo transcription measurements indicated that the alternative electron acceptors, DMSO and fumarate, could also lower ydhY-T expression, whereas trimethylamine-N-oxide (TMAO) permitted high expression. Therefore, expression of ydhY-T is subject to complex regulation in response to electron acceptor availability that involves at least three transcription factors, FNR (anaerobic activation), NarL~P (nitrate repression) and H-NS (repression in the absence of an antagonist; e.g. FNR).
authors.affiliation: Department of Molecular Biology and Biotechnology, The Krebs Institute, University of Sheffield, Sheffield S10 2TN, UK.|Present address: General Administration of Laboratories and Quality Control, Ministry of Commerce and Industry, Riyadh 11162, Kingdom of Saudi Arabia.
authors.forename: Naji
authors.initials: N
authors.lastname: Awad A Al Ibrahim
authors.affiliation: Department of Molecular Biology and Biotechnology, The Krebs Institute, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Green
mesh_terms: D000693:Anaerobiosis / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D048168:Escherichia coli K12 / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D005288:Ferredoxins / Q000235:genetics*; D005650:Fumarates / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins / Q000235:genetics* / Q000378:metabolism; D008744:Methylamines / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology*; D010088:Oxidoreductases / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D005288:Ferredoxins; D005650:Fumarates; C031908:H-NS protein, bacteria; D007506:Iron-Sulfur Proteins; D008744:Methylamines; D016877:Oxidants; C000623122:YdhT protein, E coli; C000623121:YdhY protein, E coli; C069780:NarL protein, E coli; D010088:Oxidoreductases; D012321:DNA-Directed RNA Polymerases; C005855:trimethyloxamine; D004121:Dimethyl Sulfoxide