The most widespread riboswitch class, found in organisms from all three domains of life, is responsive to the vitamin B 1 derivative thiamin pyrophosphate (TPP). We have established that a TPP-sensing riboswitch is present in the 39 untranslated region (UTR) of the thiamin biosynthetic gene THIC of all plant species examined. The THIC TPP riboswitch controls the formation of transcripts with alternative 39 UTR lengths, which affect mRNA accumulation and protein production. We demonstrate that riboswitch-mediated regulation of alternative 39 end processing is critical for TPP-dependent feedback control of THIC expression. Our data reveal a mechanism whereby metabolite-dependent alteration of RNA folding controls splicing and alternative 39 end processing of mRNAs. These findings highlight the importance of metabolite sensing by riboswitches in plants and further reveal the significance of alternative 39 end processing as a mechanism of gene control in eukaryotes.

The glmS ribozyme [1][2][3][4][5][6][7] from Bacillus cereus is a representative of a unique riboswitch class [8,9] whose members undergo selfcleavage with accelerated rate constants when bound to glucosamine-6-phosphate (GlcN6P). These metabolite-sensing ribozymes are found in numerous Gram-positive bacteria, where they control expression of the glmS gene. The glmS gene product (glutamine:fructose-6-phosphate amidotransferase) generates GlcN6P, [10,11] which binds to the ribozyme and triggers self-cleavage by internal phosphoester transfer.[1]The ribozyme is embedded within the 5' untranslated region (UTR) of the glmS messenger RNA and self-cleavage prevents production of GlmS protein, thereby decreasing the concentration of GlcN6P. The combination of molecular

The glmS ribozyme [1][2][3][4][5][6][7] from Bacillus cereus is a representative of a unique riboswitch class [8,9] whose members undergo selfcleavage with accelerated rate constants when bound to glucosamine-6-phosphate (GlcN6P). These metabolite-sensing ribozymes are found in numerous Gram-positive bacteria, where they control expression of the glmS gene. The glmS gene product (glutamine:fructose-6-phosphate amidotransferase) generates GlcN6P, [10,11] which binds to the ribozyme and triggers self-cleavage by internal phosphoester transfer.[1]The ribozyme is embedded within the 5' untranslated region (UTR) of the glmS messenger RNA and self-cleavage prevents production of GlmS protein, thereby decreasing the concentration of GlcN6P. The combination of molecular