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.