Gene activation by theEscherichia coli positive regulator OmpR: A mutational study of the DNA-binding domain of OmpR

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Abstract
TheEscherichia coli DNA-binding protein, OmpR, is one of the best characterized of the bacterial positive regulators that enhance the transcriptional ability of RNA polymerase. OmpR, consisting of 239 amino acids, binds to specific sequences located upstream of the cognateompC andompF promoters. The C-terminal half of OmpR, consisting of about 120 amino acids, exhibits an inherent DNA-binding ability. To address the issue of DNA binding by OmpR, we selected a set of OmpR mutants, each of which has a single amino acid substitution in the C-terminal half of OmpR. In particular, we characterized a number of OmpR mutants which are defective in DNA binding and thereby result in an OmpF− OmpC phenotype. Among them, a putative positive control OmpR mutant was also obtained, which appears to be defective in phosphorylation-dependent transcriptional activation, but not in DNA binding. These results are discussed with general emphasis on DNA recognition by theE. coli family of OmpR-like regulatory proteins.

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