Dynamic behaviour of the B12 riboswitch.

Riboswitches are RNA segments that serve as ligand-responsive genetic control elements. They modulate the expression of certain genes in response to changing concentrations of metabolites. In this paper, we study the dynamic behaviour of the B12 riboswitch in E. coli--perhaps the most widely studied and best known of all riboswitches--through a mathematical model of its regulatory pathway. To carry this out, we simulate dynamic experiments in which the bacterial B12 uptake capacity is measured after being depleted of this vitamin for a long time. The results of these simulations compare favourably with reported experimental data. The model also predicts that an overshoot of intracellular B12 should be observed if the replenishment experiments were to be carried out for longer times. This behaviour is discussed in terms of a possible evolutionary advantage for E. coli, together with the fact that regulation at the transcriptional and translational levels is almost equivalent dynamically.