Interaction of OmpR, a positive regulator, with the osmoregulated ompC and ompF genes of Escherichia coli. Studies with wild-type and mutant OmpR proteins.

T Mizuno,M Kato,Y L Jo,S Mizushima

doi:10.1016/s0021-9258(19)35453-5

Abstract

The OmpR protein is a positive regulator involved in osmoregulatory expression of the ompC and ompF genes that specify the major outer membrane proteins OmpC and OmpF, respectively. We purified the OmpR protein not only from wild-type cells but also from two ompR mutants (ompR2 and ompR3) exhibiting quite different phenotypes as to osmoregulation of the ompC and ompF genes. The OmpR2 protein has an amino acid conversion in the C-terminal portion of the OmpR polypeptide, whereas the OmpR3 protein has one in the N-terminal portion. Comparative studies on these purified OmpR proteins were carried out in terms of their interaction with the ompC and ompF promoters. The nucleotide sequences involved in OmpR-binding were determined in individual promoter regions by deoxyribonuclease I footprinting. The OmpR3 protein as well as the wild-type OmpR protein appeared to bind, to similar extents, to both the ompC and ompF promoters. In contrast, the OmpR2 protein bound preferentially to the ompF promoter and failed to protect the ompC promoter against DNAse I digestion. These results support the view that the C-terminal portion of the OmpR protein is responsible for the binding of the OmpR protein to the ompC and ompF promoter DNAs. Based on these results, the structure and function of the OmpR protein are discussed in relation to the mechanism of osmoregulation.

Highlights

The OmpR protein is a positive regulator involved in osmoregulatory expression of the ompC and ompF genes that specify the major outer membrane proteins OmpC and OmpF,respectively
These mutant ompR genes as well as the wild-type gene have been cloned, and theirnucleotide sequenceshave been determined to define the primary changes in the amino acid sequences of the respective mutant OmpR proteins [11].These results and those of other genetic studies on these ompR mutants supported the view that the OmpR protein has a two-domain structure, each domain playing a different role in the regulation of the ompC and ompF genes [12]
Based on the results of genetic studies, we proposed that the OmpR protein activates the ompC and ompF genes by binding to a region upstream of the -35 region of the promoters of these genes[4, 6]