Repression of the Gene Encoding Succinate Dehydrogenase in Respon to Glucose Is Mediated by the EIICBGIC Protein in Escherichia coli

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Abstract
The Escherichia colisdhCDAB operon encodes succinate dehydrogenase, an enzyme complex involved in the tricarboxylic acid (TCA) cycle. Expression of this operon is under complex transcriptional regulation in response to growth conditions, such as anaerobiosis and carbon sources. Typically, the expression of sdhCDAB is known to be subjected to “an aerobic repression” and “a glucose repression.” The molecular mechanism underlying the anaerobic repression has been well documented, involving both the ArcB-ArcA two-component system and the Fnr global anaerobic regulator. However, the mechanism underlying the glucose repression is not yet clear, because the involvment of the general catabolite regulators such as CRP and CRA has been dismissed. In this study, we conducted a series of genetic analyses to identify the regulator gene(s) involved in the glucose repression of sdh. The results demonstrate that the EIICBGIC protein (the ptsG gene product), a component of the major glucose transporter, acts as a crucial mediator in glucose repression. These results support the view that the EIICBGlc protein functions not only as a glucose transporter, but also as a glucose-sensing signal transducer that modulates the glucose repression of the sdhCDAB operon.

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