Aerobic activation of transcription of the anaerobically inducible Escherichia coli focA-pfl operon by fumarate nitrate regulator.
Expression of the anaerobically inducible focA-pfl operon in Escherichia coli was activated nearly sevenfold relative to wild-type under aerobic growth conditions by increasing the dosage of the fnr gene on a pBR322-based plasmid (pCH21). No effect on anaerobic expression levels was observed, suggesting that operon expression under these conditions is maximal. Examination of the complex transcript pattern of the focA-pfl operon confirmed that in strains bearing pCH21 all transcripts, with the exception of the promoter 7 transcript, were up-regulated aerobically. Western analysis of strains bearing pCH21 revealed that the fumarate nitrate regulator (FNR) level was increased approximately ninefold relative to the level in strains bearing a single copy of the fnr gene aerobically, but was only overproduced threefold anaerobically. Analysis of an fnr-lacZ fusion indicated that fnr expression was more strongly negatively autoregulated in anaerobic cells compared with aerobic cells when pCH21 was present. Taken together, these findings suggest that high-level overproduction of FNR is prevented anaerobically by active FNR repressing expression of the fnr gene. Furthermore, transcription from promoter 7 of the focA-pfl operon, which depends on both ArcA-P and FNR, cannot be activated aerobically by overproduction of FNR alone, while promoter 6, which is less dependent on ArcA-P, can be activated under these conditions.
Reyes-Ramírez
Francisca
F
Department of Molecular Microbiology, John Innes Centre, Norwich, UK.
Sawers
R Gary
RG
D000123:Acetyltransferases; D000332:Aerobiosis; D000693:Anaerobiosis; D004798:Enzymes / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009876:Operon; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic
D004798:Enzymes; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; C088103:FocA protein, E coli; D007506:Iron-Sulfur Proteins; D026901:Membrane Transport Proteins; D000123:Acetyltransferases; C040285:pyruvate formate-lyase activating enzyme