Regulation of the early steps of 3-phenylpropionate catabolism in Escherichia coli

Microbial catabolism of phenylpropanoid compounds plays a key role in the degradation of aromatic molecules originating from the degradation of proteins and plant constituents. In this study, the regulation of the early steps in the utilisation of 3-phenylpropionate, a phenylpropanoid compound, was investigated. Expression of the hcaA gene product, which is involved in 3-phenylpropionate catabolism in Escherichia coli, was positively regulated by HcaR, a regulatory protein similar to members of the LysR regulators family. Remarkably, the expression of hcaA in the presence of 3-phenylpropionate was sharply and transiently induced at the end of the exponential growth phase. This occurred in a rpoS-independent manner. This transient induction was also mediated by HcaR. The expression of this positive regulator is negatively autoregulated, as for other members of the LysR family. The expression of hcaR is strongly repressed in the presence of glucose. Glucose-dependent repression of hcaR expression could only be partially overcome by adding exogenous cAMP.     

Location of phosphorylation site and DNA-binding site of a positive regulator, OmpR, involved in activation of the osmoregulatory genes of Escherichia coli

The OmpR protein of Escherichia coli is a positive regulator involved in activation of the ompF and ompC genes which encode the major outer membrane proteins OmpF and OmpC, respectively. By employing recombinant DNA techniques, we isolated the N- and C-terminal halves of the OmpR molecule. From the results of biochemical analyses of these fragments, it was concluded that the N-terminal portion contains a site involved in phosphorylation by an OmpR-specific protein kinase EnvZ, whereas the C-terminal part possesses a DNA-binding site for the ompC and ompF promoters.