CHARACTERIZATION OF THE BACILLUS-SUBTILIS THIC OPERON INVOLVED IN THIAMINE BIOSYNTHESIS

The characterization of a three-gene operon (the thiC operon) at 331 m in, which is involved in thiamine biosynthesis in Bacillus subtilis, i s described. The first gene in the operon is homologous to transcripti on activators in the lysR family. The second and third genes (thiK and thiC) have been subcloned and overexpressed in Escherichia coli, ThiK (30 kDa) catalyzes the phosphorylation of 4-methyl-5-(beta-hydroxythy l)thiazole. ThiC (27 kDa) catalyzes the substitution of the pyrophosph ate of 2-methyl-4-amino-5-hydroxymethylpyrimidine pyrophosphate pyroph osphate by 4-methyl-5-(beta-hydroxyethyl)thiazole phosphate to yield t hiamine phosphate. Transcription of the thiC operon is not regulated b y thiamine or 2-methyl-4-amino-5-hydroxymethylpyrimidine and is only s lightly repressed by 4-methyl-5-(beta-hydroxyethyl)thiazole.