Cross-induction of glc and ace operons of Escherichia coli attributable topathway intersection - Characterization of the glc promoter

The metabolic pathways specified by the glc and ace operons in Escherichia coli yield glyoxylate as a common intermediate, which is acted on by two ma late synthase isoenzymes: one encoded by glcB and the other by aceB. Null m utations in either gene exhibit no phenotype, because of cross-induction of the ace operon by glycolate and the glc operon by acetate. In this study, the regulation of the glc operon, comprising the structural genes glcDEFGB, was analyzed at the molecular level. This operon, activated by growth on g lycolate, is transcribed as a single message and is under the positive cont rol of GlcC encoded by a divergent gene. Expression of the glc operon is st rongly dependent on the integration host factor (IHF) and is repressed by t he global respiratory regulator ArcA-P, In vitro gel-shift experiments demo nstrated direct binding of the promoter DNA to IHF and ArcA-P. Mutant analy sis indicated that cross-induction of the glc operon by acetate is mediated by the GlcC protein that recognizes the compound as an alternative effecto r. The similar pattern of regulation of the Glc and Ace systems by IHF and ArcA-P ensures their effective cross-induction.