Escherichia coli mhpR gene expression is regulated by catabolite repression mediated by the cAMP–CRP complex

Abstract

The expression of themhpgenes involved in the degradation of the aromatic compound 3-(3-hydroxyphenyl)propionic acid (3HPP) inEscherichia coliis dependent on the MhpR transcriptional activator at thePapromoter. This catabolic promoter is also subject to catabolic repression in the presence of glucose mediated by the cAMP–CRP complex. ThePrpromoter drives the MhpR-independent expression of the regulatory gene.In vivoandin vitroexperiments have shown that transcription from thePrpromoter is downregulated by the addition of glucose and this catabolic repression is also mediated by the cAMP–CRP complex. The activation role of the cAMP–CRP regulatory system was further investigated by DNase I footprinting assays, which showed that the cAMP–CRP complex binds to thePrpromoter sequence, protecting a region centred at position −40.5, which allowed the classification ofPras a class II CRP-dependent promoter. Open complex formation at thePrpromoter is observed only when RNA polymerase and cAMP–CRP are present. Finally, byin vitrotranscription assays we have demonstrated the absolute requirement of the cAMP–CRP complex for the activation of thePrpromoter.