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J. Biol. Chem., Vol. 278, Issue 51, 50978-50984, December 19, 2003

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A Fraction of the BglG Transcriptional Antiterminator from Escherichia coli Exists as a Compact Monomer^*

Liat Fux, Anat Nussbaum-Shochat, and Orna Amster-Choder

From the Department of Molecular Biology, The Hebrew University, Hadassah Medical School, P. O. Box 12272, Jerusalem 91120, Israel

Expression of the bgl operon in Escherichia coli, induced by -glucosides, is positively regulated by BglG, a transcriptional antiterminator. In the presence of inducer, BglG dimerizes and binds to the bgl transcript to prevent premature termination of transcription. The dimeric state of BglG is determined by BglF, a membrane-bound enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system (PTS), which reversibly phosphorylates BglG according to -glucoside availability. BglG is composed of an RNA-binding domain followed by two homologous PTS regulation domains (PRD1 and PRD2). The predicted structure of dimeric LicT, a BglG homologue from Bacillus subtilis, suggests that the two PRDs adopt a similar structure and that the interactions within the dimer are PRD1-PRD1 and PRD2-PRD2. We have shown recently that the PRD1 and PRD2 domains of BglG can form a stable heterodimer. We report here, based on in vitro and in vivo cross-linking experiments, that a fraction of BglG is present in the cell in a compact form in which PRD1 and PRD2 are in close proximity. The compact form is present mainly in the BglG monomers. Our results imply that the monomer-dimer transition involves a conformational change. The possible role of the compact form in preventing untimely induction of the bgl operon is discussed.

Received for publication, July 24, 2003 , and in revised form, September 25, 2003.

^* This research was supported by the Israel Science Foundation founded by the Israel Academy of Sciences and Humanities and by United States-Israel Binational Science Foundation (BSF) Grant 1999344. 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.

To whom correspondence should be addressed. Tel.: 972-2-675-8460; Fax: 972-2-6784010; E-mail: amster{at}cc.huji.ac.il.

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