Dual control by regulators, GntH and GntR, of the GntII genes for gluconate metabolism in Escherichia coli

Escherichia coli possesses two systems, GntI and GntII, for gluconate uptake and catabolism, whose genes are regulated by GntR as a repressor and GntH as an activator, respectively. Additionally, GntH exerts negative control of the GntI genes via the same binding element as that of GntR. We thus examined whether GntR involves regulation of the GntII genes or not. This regulation and the control by GntH were examined by using single-copy LACZ operon fusions and by RT-PCR, suggesting positive and negative regulation by GntR and positive regulation by GntH. Moreover, the introduction of mutations into possible GntR-binding elements revealed that both regulators share at least one of the elements. The results presented allow us to speculate that GntR initiates expression of the GntII genes, followed by their large induction by GntH when cells were grown in gluconate minimum medium. As in the case of the GntI genes, such a cross-regulation between the GntI and GntII via the two regulators may be important for cells to grow with gluconate.