title: A fraction of the BglG transcriptional antiterminator from Escherichia coli exists as a compact monomer.
abstract: Expression of the bgl operon in Escherichia coli, induced by beta-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 beta-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.
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D003432:Cross-Linking Reagents; D003545:Cysteine; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics; D009154:Mutation; D009876:Operon; D017434:Protein Structure, Tertiary; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; D016601:RNA-Binding Proteins; C064872:antiterminator proteins, Bacteria; D003545:Cysteine