Abstract
We have investigated the interaction between BgIF and BgIG, two proteins that regulate expression of the E. coli bgI operon. BgIF is both a negative regulator of operon expression and a phosphotransferase involved in uptake of β-glucosides. BgIG is a positive regulator that functions as a transcriptional antiterminator. We show here that BgIF is phosphorylated by the soluble components of the phosphotransferase system: Enzyme I, HPr, and the phosphate donor phosphoenolpyruvate. Phosphorylated BgIF can then transfer phosphate either to β-glucosides or to wild-type BgIG. Mutant BgIG derivatives, which give constitutive expression of the bgI operon, show little or no phosphorylation by BgIF. Hence BgIF exerts its negative effect on operon expression by phosphorylating BgIG, blocking its action as an antiterminator. BgIG is dephosphorylated only in the presence of both BgIF and β-glucosides. Based on these results, we propose the following mechanism: In the absence of β-glucosides, BgIG is phosphorylated by BgIF and is inactive in antitermination. Addition of inducer stimulates BgIF to dephosphorylate BgIG, allowing BgIG to function as a positive regulator of operon expression. β-Glucosides are then phosphorylated and transported into the cell by BgIF.
| Original language | English |
|---|---|
| Pages (from-to) | 847-855 |
| Number of pages | 9 |
| Journal | Cell |
| Volume | 58 |
| Issue number | 5 |
| DOIs | |
| State | Published - 8 Sep 1989 |
| Externally published | Yes |
Bibliographical note
Funding Information:Polaczek, and S. Langerman for critically reading the manuscript and for fruitful discussions. We thank Dr. Gary Jacobson and Sanjay Khan-dekar for advice on the in vitro system and for the gift of strains. We thank Rina Ben Yaacov for preparing the figures. This work was supported by National Institutes of Health grant GM38035. 0. A.-C. was supported by a postdoctoral fellowship from the European Molecular Biology Organization. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.