Department of Genetics, Washington University School of Medicine, 660 S. Euclid, St. Louis, MO 63110, USA.
Riboswitches are mRNAs that can act as direct sensors of small molecules to control their own expression. In the May 30, 2003, issue of Cell, Mandal et al. show that cis elements in mRNAs involved in purine metabolism measure the effector molecule concentration with sensitivity and specificity, and control expression of adjacent genes. Analysis of several recently discovered riboswitches suggests that this may be a common, efficient mechanism for regulating the synthesis of proteins required for the production of important metabolites.