Download MendeleyAn excited state underlies gene regulation of a transcriptional riboswitch.
Zhao, B., Guffy, S.L., Williams, B., Zhang, Q.(2017) Nat Chem Biol 13: 968-974
- PubMed: 28719589
- DOI: https://doi.org/10.1038/nchembio.2427
- Primary Citation of Related Structures:
5KH8 - PubMed Abstract:
Riboswitches control gene expression through ligand-dependent structural rearrangements of the sensing aptamer domain. However, we found that the Bacillus cereus fluoride riboswitch aptamer adopts identical tertiary structures in solution with and without ligand. Using chemical-exchange saturation transfer (CEST) NMR spectroscopy, we revealed that the structured ligand-free aptamer transiently accesses a low-populated (∼1%) and short-lived (∼3 ms) excited conformational state that unravels a conserved 'linchpin' base pair to signal transcription termination. Upon fluoride binding, this highly localized, fleeting process is allosterically suppressed, which activates transcription. We demonstrated that this mechanism confers effective fluoride-dependent gene activation over a wide range of transcription rates, which is essential for robust toxicity responses across diverse cellular conditions. These results unveil a novel switching mechanism that employs ligand-dependent suppression of an aptamer excited state to coordinate regulatory conformational transitions rather than adopting distinct aptamer ground-state tertiary architectures, exemplifying a new mode of ligand-dependent RNA regulation.
Organizational Affiliation:
Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
