Activation of the osmoregulated ompF and ompC genes by the OmpR protein in Escherichia coli: a study involving chimeric promoters.

Abstract

The expression of each of the Escherichia coli ompF and ompC genes is activated by the common positive regulator, OmpR, in response to the medium osmolarity. The promoters for these genes consist of canonical -35 and -10 regions, and upstream OmpR-binding sites. In this study, we constructed a functional ompF-ompC chimeric promoter consisting of the OmpR-binding site of ompF, and the -35 and -10 regions of ompC, which was fused to the lacZ gene on a low-copy-number plasmid. It is known that the ompF and ompC genes are expressed in a different manner in cells with mutations in the ompR gene. In this respect, it was found that the ompF-ompC chimeric promoter behaves just like ompF promoter with respect to an ompR mutation (ompR472). It was revealed that, in this chimeric promoter, the OmpR-binding site must be located stereospecifically with respect to the -35 and -10 regions for OmpR-dependent transcription of the ompF-ompC chimeric promoter to occur. These results are discussed in relation to the structures and functions of the ompF and ompC promoters, the occurrence of a DNA curvature in the promoter regions being implied, which may be an important parameter for the transcription activation by the OmpR protein.