Effects of Carbon Source on Expression of F o Genes and on the Stoichiometry of the c Subunit in the F 1 F o ATPase of Escherichia coli

Abstract

ABSTRACT Expression of the genes for the membrane-bound F o sector of the Escherichia coli F 1 F o proton-translocating ATPase can respond to changes in metabolic conditions, and these changes are reflected in alterations in the subunit stoichiometry of the oligomeric F o proton channel. Transcriptional and translational lacZ fusions to the promoter and to two F o genes show that, during growth on the nonfermentable carbon source succinate, transcription of the operon and translation of uncB , encoding the a subunit of F o , are higher than during growth on glucose. In contrast, translation of the uncE gene, encoding the c subunit of F o , is higher during growth on glucose than during growth on succinate. Translation rates of both uncB and uncE change as culture density increases, but transcription rates do not. Quantitation of the c stoichiometry shows that more c subunits are assembled into the F 1 F o ATPase in cells grown on glucose than in cells grown on succinate. E. coli therefore appears to have a mechanism for regulating the composition and, presumably, the function of the ATPase in response to metabolic circumstances.