Fig. 4

Structure and genetic context of the thiS motif. a Consensus sequence and secondary structure model for the thiS motif. Annotations are as described for Fig. 3. The P0 stem is predicted to exist if the lower portion of P1 fails to form. b (Top) Distribution of gene associations for the ~ 700 thiS motif representatives in bacteria. The chart incorporates the first five genes downstream of the thiS motif, and has a total of 1922 entries. These genes, which are typically in the thiS operon, are counted individually. (Bottom) Protein products of the genes abbreviated here, when known, catalyze the reaction steps for thiamin biosynthesis depicted in c. c The biosynthetic pathway of TPP in Bacillus subtilis. Acronyms starting from the top left are: aminoimidazole ribotide (AIR), hydroxymethyl-pyrimidine (HMP) hydroxymethyl-pyrimidine phosphate (HMP-P), hydroxymethyl-pyrimidine pyrophosphate (HMP-PP), hydroxyethyl-thiazole (HET), hydroxyethyl-thiazole phosphate (HET-P), thiamin monophosphate (TMP), and thiamin pyrophosphate (TPP). TMP (green shaded box) is formed by fusing the two compounds HMP-PP (blue shaded box) and HET-P (gold shaded box). Note that both HET-P and TPP can be synthesized through a salvage pathway starting with HET and thiamin, respectively. HMP-PP and HET-P were proposed as the top ligand candidates for the thiS riboswitch candidate. Metabolic scheme is based on that published previously [56]