Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Thursday Speaker Abstracts

SINGLE-MOLECULE SPECTROSCOPY OF DISORDERED REGIONS AND NUCLEIC ACIDS IN BACTERIAL TRANSCRIPTION Andrea Soranno ; 1 Washington University in St. Louis - Saint Louis, MO, Biochemistry and Molecular Biophysics, Saint Louis, MO, USA Our lab uses single-molecule spectroscopy to study how intrinsically disordered regions (IDRs) regulate biological function and disease, from cardiac proteins to viral genome packaging and bacterial transcription. In this talk, I focus on sigma factors ( σ ), which enable RNA polymerase (RNAP) to initiate transcription. In Mycobacterium tuberculosis, the housekeeping σ A contains a ~200-amino-acid N-terminal IDR with highly segregated charges. Removing this IDR strongly reduces transcription under multi-round conditions, suggesting a role in RNAP holoenzyme formation and recycling. Using fluorescence correlation spectroscopy (FCS) and single-molecule FRET, we find that the IDR enhances RNAP binding, adopts salt-dependent conformations, and remains highly dynamic in both free and bound states. Notably, it expands upon RNAP binding but re-compacts in the transcriptionally competent complex. Our results show that σ A–RNAP– DNA assembly competes with non-specific DNA interactions and suggest that conserved IDR sequence features across Actinobacteria provide a general mechanism for modulating bacterial transcription.

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