Identification of the DNA-binding domain of the OmpR protein required for transcriptional activation of the ompF and ompC genes of Escherichia coli by in vivo DNA footprinting.

Expression of the ompF and ompC genes of Escherichia coli requires the OmpR protein for transcriptional activation. In vivo binding of the OmpR protein to the ompF and ompC promoter regions was observed using an in vivo dimethyl sulfate DNA footprinting technique. Two different sequence motifs were found to be protected by OmpR in both the ompF and ompC promoter regions. This technique was further used to localize the DNA-binding domain of OmpR to be within the C-terminal 117 amino acid residues. Binding of the C-terminal portion OmpR to the ompF and ompC promoter regions, however, did not result in activation of transcription. Our results, together with sequence homologies between OmpR and other regulatory proteins, suggests that OmpR has separable domain structures: the C-terminal portion for binding-specific DNA sequences and the N-terminal portion for interacting with RNA polymerase and/or other transcription factors.