Kinetic regulation mechanism of pbuE riboswitch.

Riboswitches are RNA residue segments located in untranslated regions of messenger RNAs. These folded segments directly bind ligands through shape complementarity and specific interactions in cells and alter the expression of genes at the transcriptional or translational level through conformation change. Using the recently developed systematic helix-based computational method to predict the cotranscription folding kinetics, we theoretically studied the cotranscription folding behavior of the Bacillus subtilis pbuE riboswitch in the absence and presence of the ligand. The ligand concentration, the transcription speed, and the transcription pausing are incorporated into the method. The results are in good agreement with the experimental results. We find that there are no obvious misfolded structures formed during the transcription and the formation of the ligand bound state is rate-limited by the association of the ligand and the RNA. For this kinetically driven riboswitch, the ligand concentration, the transcription speed, and the transcription pausing are coupled to perform regulatory activity.