Regulation of transcription elongation is widely used by bacteria; however, most of our knowledge of these genetic mechanisms is derived from Escherichia coli . In E. coli , transcription and translation are coupled through a NusG-S10 interaction bridge. These proteins also participate in the formation of an antitermination complex that affects ribosomal RNA operons ( rrn ). In both complexes, the binding of S10 to the C-terminal domain of NusG blocks the Rho termination factor from accessing RNA polymerase, thereby inhibiting transcription termination. Ribosomal protein S10 also binds to the NusB protein, and NusB subsequently binds to boxA, a specific RNA sequence on the nascent RNA. These interactions are thought to nucleate the formation of the rrn antitermination complex. In contrast, Bacillus subtilis , a Gram-positive model organism in which Rho and NusG are dispensable for viability, lacks transcription-translation coupling, and ribosomal antitermination has not been previously demonstrated in this species. These differences raise important questions regarding interactions that affect elongation control mechanisms. To address this, we investigated protein-protein and protein-RNA interactions that underlie ribosomal antitermination in B. subtilis . Specifically, we combined nuclear magnetic resonance spectroscopy and isothermal titration calorimetry to assess whether the interactions used by E. coli antitermination complexes also occur in B. subtilis homologs. Our data reveal binding among NusB, S10, NusG, and boxA RNA, providing the first structural evidence that Gram-positive bacteria assemble a ribosomal antitermination complex. This work explores the structural importance of ribosomal antitermination in Gram-positive bacteria and provides new insight into bacterial transcription regulation beyond the paradigm of E. coli.
Thao N.P. Tran (Sun,) studied this question.