Riboswitches: Nature’s Chemical Sensors and Switches Made of RNA
Riboswitches are natural RNA structures that selectively bind metabolites or ions and regulate the expression of numerous genes. Approximately 40 distinct classes have been experimentally validated in diverse bacterial species. Intriguingly, derivatives of RNA monomers are the most common types of ligands sensed by riboswitches, suggesting that many of the classes discovered to date are of ancient origin. Recently, riboswitches have been discovered for ligands ranging from widespread signaling molecules to toxic chemicals, which have also revealed hidden pathways important for promoting physiological change or for detoxifying the cellular environment. Some of these recent discoveries will be presented, along with a surprising projection of the total number of riboswitch classes that remain to be discovered. This estimate suggests that there are a large number of novel riboswitch classes in bacteria that sense a far greater diversity of chemical targets.