Transcription Regulation of ompF and ompC by a Single Transcription Factor, OmpR

Abstract

The ompF and ompC genes of Escherichia coli are reciprocally regulated by a single transcription factor, phosphorylated OmpR (OmpR-P), depending upon medium osmolarity. This regulation involves activation of ompF and its repression with concomitant activation of ompC. This occurs through OmpR-P binding to four (F1, F2, F3, and F4) and three (C1, C2, and C3) sites located upstream of the ompF and ompC promoters, respectively, through a novel mechanism. Here we show that there is a distinct OmpR-P binding hierarchy within F1, F2, and F3 sites as well as within C1, C2, and C3 sites. Each of these sites contains two tandem 10-bp OmpR-P-binding subsites, a-site and b-site (from 5 to 3 direction). OmpR-P has higher affinity to the downstream b-site than to the upstream a-site in each case. Six OmpR-P molecules bind to F and C sites two-by-two in a discontinuous "galloping" manner. We propose that this tight hierarchical binding of a transcription factor, OmpR, allows distinct stepwise regulation of ompF and ompC transcription, which minimizes their overlapping expression upon changes in the medium osmolarity to achieve the reciprocal expression of ompF and ompC.

Positive regulation of flhDC expression by OmpR in Yersinia pseudotuberculosis

“…We also compared the interaction of OmpR and the flhDC promoter in the presence and absence of acetyl-P, and a weaker interaction was observed when OmpR was not phosphorylated (data not shown), which suggests that the regulation of flhDC expression by OmpR is not only direct but also enhanced by OmpR phosphorylation. This result is consistent with a report showing that the regulatory link between OmpR and outermembrane proteins is enhanced by OmpR phosphorylation (Yoshida et al, 2006).…”

“…OmpR positively regulates the expression of outermembrane proteins in E. coli by directly binding to promoter regions (Yoshida et al, 2006). In addition to DNA binding, OmpR was shown to interact productively with RNA polymerase to effectively regulate its transcription (Bowrin et al, 1994).…”

“…Studies of OmpR regulation are mainly focused on its roles in the regulation of virulence factors and outermembrane proteins (Brzostek et al, 2007;Yoshida et al, 2006). OmpR has also been shown to regulate flagellar gene regulation.…”

“…Two regions around the promoter, named O 1 and O 2 (Fig. 2a), were highly similar to the conserved OmpR-binding sequence reported in E. coli (Egger et al, 1997;Yoshida et al, 2006). In the present study, we named the DNA fragment from +150 to 2150, which contains both the O 1 and O 2 sites, the Y-OF segment (Fig.…”

PhoB transcriptional activator binds hierarchically to pho box promoters

“…The lower affinity of PhoB for this second sequence is compensated by protein-protein interactions between dimers, more likely when the DNA is bent (Blanco et al , 2002 ) than when it is in a more extended form (as in the current structure). A hierarchical binding was already described for the ortholog OmpR and its functional relevance in the alternative activation and repression of the genes that code for two porins to control cellular osmolarity was deciphered (Slauch and Silhavy , 1989 ;Rampersaud et al , 1994 ;Huang et al , 1997 ;Head et al , 1998 ;Yoshida et al , 2006 ). PhoB binding to the pho box promoter sequence leads to the recruitment of RNA polymerase.…”