Fig. 5.

Model of transcription termination control by the mgtCBR leader. (A) Schematic of the DNA region corresponding to the mgtCBR leader. Small ORFs are indicated by pink and white arrows; the position of RARE and rut are indicated by rectangles, and transcription pause sites (Fig. 2C) by open boxes. The leader RNA emerges from the transcribing RNAP and folds into stem-loop A. (B) When translation is efficient, the ribosome translating mgtM unwinds stem-loop A, allowing folding of stem-loop B, which sequesters RARE. Rho loads onto the RNA and translocates toward a paused RNAP. Rho triggers transcription termination, thereby turning mgtCBR expression OFF. (C) When translation is inefficient, single-stranded RARE traps Rho in an inactive state. Transcription continues, turning mgtCBR expression ON.