Mechanism and distribution of glmS ribozymes.

Among the nine classes of ribozymes that have been experimentally validated to date is the metabolite-responsive self-cleaving ribozyme called glmS. This RNA is almost exclusively located in the 5'-untranslated region of bacterial mRNAs that code for the production of GlmS proteins, which catalyze the synthesis of the aminosugar glucosamine-6-phosphate (GlcN6P). Each glmS ribozyme forms a conserved catalytic core that selectively binds GlcN6P and uses this metabolite as a cofactor to promote ribozyme self-cleavage. Metabolite-induced self-cleavage results in down-regulation of glmS gene expression, and thus the ribozyme functions as a key riboswitch component to permit feedback regulation of GlcN6P levels. Representatives of glmS ribozymes also serve as excellent experimental models to elucidate how RNAs fold to recognize small molecule ligands and promote chemical transformations.