Sequence‐dependent folding and unfolding of ligand‐bound purine riboswitches |
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Authors: | Oksana Prychyna Michael S. Dahabieh Jay Chao Melanie A. O'Neill |
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Affiliation: | Department of Chemistry, Simon Fraser University, Burnaby, B.C., Canada, V5A 1S6 |
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Abstract: | Riboswitch regulation of gene expression requires ligand‐mediated RNA folding. From the fluorescence lifetime distribution of bound 2‐aminopurine ligand, we resolve three RNA conformers (Co, Ci, Cc) of the liganded G‐ and A‐sensing riboswitches from Bacillus subtilis. The ligand binding affinities, and sensitivity to Mg2+, together with results from mutagenesis, suggest that Co and Ci are partially unfolded species compromised in key loop‐loop interactions present in the fully folded Cc. These data verify that the ligand‐bound riboswitches may dynamically fold and unfold in solution, and reveal differences in the distribution of folded states between two structurally homologous purine riboswitches: Ligand‐mediated folding of the G‐sensing riboswitch is more effective, less dependent on Mg2+, and less debilitated by mutation, than the A‐sensing riboswitch, which remains more unfolded in its liganded state. We propose that these sequence‐dependent RNA dynamics, which adjust the balance of ligand‐mediated folding and unfolding, enable different degrees of kinetic discrimination in ligand binding, and fine‐tuning of gene regulatory mechanisms. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 953–965, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com |
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Keywords: | riboswitches RNA folding mutagenesis 2‐aminopurine time‐resolved fluorescence |
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