Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Thursday Speaker Abstracts

SYNC OR SINK: THE EXTENT OF TRANSCRIPTION-TRANSLATION COUPLING DETERMINES TRANSCRIPTION FACTOR RECRUITMENT TO REGULATE GENE EXPRESSION Nusrat Qureshi 1 ; Olivier Duss 1 ; 1 European Molecular Biology Laboratory (EMBL), Molecular Systems Biology, Heidelberg, Germany In bacteria, transcription and translation occur in the same cellular compartment and thus, can physically and functionally be coupled. We recently demonstrated that the ribosome can activate a paused RNAP by long-range interactions, mediated by mRNA looping (Qureshi & Duss, Nature, 2025). However, it is not clear how transcription factors of opposing function such as NusA (mediating transcription pausing), NusG (promoting transcription elongation) and Rho (inducing transcription termination) are specifically recruited to either interfere or cooperate with the different states of the transcription-translation machinery, especially as all factors are present simultaneously. Here, using multicolor single-molecule FRET we show that NusA, NusG and Rho dynamically associate with transcription-translation coupled (TC-TL) complexes on a seconds-timescale. Importantly, these factors detect the degree of machine coupling by tuning their dwell time to either shut down unproductive TC-TL complexes or promote transcription. For instance, the pause-promoting NusA factor preferentially targets early transcription elongation complexes, where it possibly acts as a regulatory brake to allow time for ribosome loading, but is occluded from tightly coupled TC-TL complexes. NusG, shows increased lifetimes after a coupled ribosome has joined, relevant for maintaining machine coupling throughout the gene for boosting transcription efficiency. Rho efficiently shuts down unproductive transcription elongation complexes, without a translating ribosome. However, it can also access the looped-out mRNA of loosely coupled TC-TL complexes, when the gap between the machines grows too large. Overall, by tracking the activity of the coupled transcription-translation machinery in various states and simultaneously transcription factors recruitment in real-time, our study reveals how the transcription factor interaction efficiency provides a means to only engage the relevant transcription factors with the respective functional TC-TL complexes.

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