Gene Regulation by Riboswitches

Riboswitches are structured RNAs usually located in the untranslated regions (UTRs) of bacterial mRNAs that bind metabolites and control gene expression. We have recently examined a series of riboswitches that carry newfound aptamer structures and that control gene expression using previously uncharacterized mechanisms. For example, several riboswitch classes have been discovered that sense the coenzyme S‐adenosylmethionine (SAM) and discriminate against the demethylated analog S‐adenosylhomocysteine (SAH). However, we have discovered a widespread riboswitch class that preferentially recognizes SAH versus SAM, and controls genes required to recycle SAH. We also have identified a large and well‐conserved RNA element that functions as a riboswitch for molybdenum coenzyme (Moco). These findings indicate that numerous metabolite‐sensing riboswitches likely remain undiscovered. Furthermore, we have determined that some mRNAs in eukaryotes use riboswitches to control alternative splicing. The diversity of riboswitch aptamer types and the diversity of mechanisms used by these molecular switches to control gene expression demonstrate the enormous structural and functional potential of RNA that is harnessed by modern organisms.