THE GLOBAL REGULATORY PROTEIN FRUR MODULATES THE DIRECTION OF CARBON FLOW IN ESCHERICHIA-COLI

Escherichia coli fructose repressor, FruR, is known to regulate expres sion of several genes concerned with carbon utilization. Using a previ ously derived consensus sequence for FruR binding, additional potentia l operators were identified and tested for FruR binding in DNA band mi gration retardation assays. Operators in the control regions of operon s concerned with carbon metabolism bound FruR, while those in operons not concerned with carbon metabolism did not. In vivo assays with tran scriptional lacZ fusions showed that FruR controls the expression of F ruR operator-containing genes encoding key enzymes of virtually every major pathway of carbon metabolism. Moreover, a fruR null mutation alt ered the rates of utilization of at least 36 carbon sources. In genera l, oxidation rates for glycolytic substances were enhanced while those for gluconeogenic substances were depressed. Alignment of FruR operat ors revealed that the consensus sequence for FruR binding is the same for operons that are activated and repressed by FruR and permitted for mulation of a revised FruR-binding consensus sequence. The reported ob servations indicate that FruR modulates the direction of carbon flow b y transcriptional activation of genes encoding enzymes concerned with oxidative and gluconeogenic carbon flow and by repression of those con cerned with fermentative carbon flow.