A model of kinetically controlled riboswitches

This cartoon shows a kinetically controlled riboswitch that regulates mRNA transcription. RNA polymerase (orange circle) transcribes the aptamer domain of a riboswitch (black) prior to transcription of the expression platform. A pause site (purple star) causes RNA polymerase to stall on the DNA template (green). The observed rate of ligand binding to the aptamer domain (kobs) is approximately equal to the rate constant associated with ligand binding (kon) multiplied by the ligand concentration ([M]). The rate of RNA folding (kF) in response to ligand binding must occur before RNA polymerase can fully transcribe the expression platform (kTx). The antiterminator and terminator stem-loops are labeled AT and T, respectively.