Structure of the S-adenosylmethionine riboswitch regulatory mRNA element.

Genes are commonly turned on or off by protein factors that respond to cellular signals. The recent discovery of riboswitches, regulatory elements within some messenger RNAs, proved that RNA can also detect essential metabolites and control genes. Two structural studies throw new light on the riboswitch system. Serganov et al. use X-ray diffraction to establish the three-dimensional structure of a riboswitch from Escherichia coli bound to its target, a vitamin B1 derivative. These findings reveal how RNA folds to form a precise pocket for its target and how the antibiotic pyrithiamine acts by tricking the riboswitch. This suggests a new drug design strategy for antibacterials and antifungals targeting riboswitches. Montange and Batey have solved the structure of a bacterial riboswitch RNA bound to S-adenosyl methionine. Its complex folded structure reveals how ligand binding leads structural changes that prevent further transcription.