An Autoinhibited State in the Structure of Thermotoga maritima NusG

SummaryNusG is a conserved regulatory protein interacting with RNA polymerase (RNAP) and other proteins to form multicomponent complexes that modulate transcription. The crystal structure of Thermotoga maritima NusG (TmNusG) shows a three-domain architecture, comprising well-conserved amino-terminal (NTD) and carboxy-terminal (CTD) domains with an additional, species-specific domain inserted into the NTD. NTD and CTD directly contact each other, occluding a surface of the NTD for binding to RNAP and a surface on the CTD interacting either with transcription termination factor Rho or transcription antitermination factor NusE. NMR spectroscopy confirmed the intramolecular NTD-CTD interaction up to the optimal growth temperature of Thermotoga maritima. The domain interaction involves a dynamic equilibrium between open and closed states and contributes significantly to the overall fold stability of the protein. Wild-type TmNusG and deletion variants could not replace endogenous Escherichia coli NusG, suggesting that the NTD-CTD interaction of TmNusG represents an autoinhibited state.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (123 K)Download as PowerPoint slideHighlights► Thermotoga maritima NusG shows a dynamic intramolecular NTD-CTD interaction ► The NTD-CTD interaction hides the binding surfaces for RNA polymerase, S10, and Rho ► Domain interaction contributes to thermostability ► Thermotoga maritima NusG does not complement a NusG-deficient E. coli strain