Abstract
Expression of the ompF gene, which is under the control of the OmpR protein, is regulated by the osmolarity of the medium. To study the mechanism of osmoregulation, plasmids carrying two different types of chimeric genes were constructed. In one type, the coding region of the ompF gene was linked to the trp promoter (trpPO) preceding ompF, and in the other type the ompF upstream region, mostly composed of the region for regulation by OmpR and the promoter region, was linked to the lacZ gene by protein fusion. Expression of beta-galactosidase by the lacZ chimeric gene was OmpR dependent and osmoregulated as sensitively as that of the intact ompF gene. In the ompR20 background the direction of osmoregulation was opposite that of normal osmoregulation, as was the direction of osmoregulation of the intact ompF gene. Osmoregulation was also observed with trpPO-ompF chimeric genes. However, the regulation was not as sensitive to the osmolarity of the medium as was regulation of the intact ompF gene and was independent of OmpR. These results suggest that OmpR-dependent osmoregulation played a primary role in the osmoregulation of ompF expression and that ompR-independent osmoregulation most likely did not play a crucial role. Studies with a series of trpPO-ompF chimeric genes also suggest that the untranslated leader region, about 100 base pairs in length, between the transcription initiation site and the initiation codon was not required for osmoregulation.