Stereospecific positioning of the cis-acting sequence with respect to the canonical promoter is required for activation of the ompC gene by a positive regulator, OmpR, in Escherichia coli.

Expression of the ompC gene coding for a major outer-membrane protein of Escherichia coli is regulated by a transcriptional activation mechanism that requires the ompR gene product, OmpR. It was demonstrated that multiple OmpR molecules bind to a cis-acting sequence located upstream from the canonical -35 and -10 regions of the ompC promoter. Using an ompC-lacZ fusion gene, the distance between the cis-acting upstream sequence (OmpR-binding site) and the -35 and -10 regions (RNA polymerase-binding site) has been changed. We demonstrated that the ompC transcription was activated in an OmpR-dependent manner even when the cis-acting upstream sequence was separated from the -35 and -10 regions by several turns of the DNA helix, providing that the distance between them was a near-integral multiple of one turn of the DNA helix. Evidence is presented that stereospecific positioning of the cis-acting upstream sequence with respect to the canonical promoter is required for activation of the ompC gene by the positive regulator, OmpR.