Regulation of the ompC gene of Escherichia coli. Involvement of three tandem promoters.

ompC expression in Escherichia coli K-12 is known to be regulated by the ompB locus, comprising the ompR and envZ genes, and the OmpR protein is believed to act as a positive transcriptional factor. We examined the transcriptional capability of the ompC gene in vitro and found that RNA polymerase could transcribe ompC without a requirement for other transcriptional factors. Furthermore, transcripts from three tandem promoters in ompC were identified in vitro. We employed oligonucleotide-directed site-specific mutagenesis to dissect the promoter region of the gene and assayed the promoters separately for transcriptional ability using fusions to the lacZ gene. The levels of beta-galactosidase indicate that ompC expression in vivo is dependent on the function of at least one of the upstream promoters. The function of OmpR appears to be the enhancement of a basal level of ompC expression. From the results of our experiments, the site of action of OmpR was deduced to be in the vicinity of the upstream promoters of ompC.