Biosynthesis of thiamin-binding proteins in developing sesame seeds

The formation of thiamin-binding proteins (TBPs) from sesame (Sesamum indicum L.) seeds (STBP-I, -II and -III) in developing seeds was investigated. Elution profiles of STBPs obtained from seeds at 4 to 6 weeks after flowering from the Q-Sepharose Fast Flow column showed that only one STBP was contained in the seeds at 4 weeks, and two STBPs were contained in the seeds at 5 weeks, and all three STBPs were contained in the seeds at 6 weeks as well as in mature seeds. SDS-PAGE of those STBPs demonstrated that STBP in the seeds at 4 weeks was large STBP termed as STBP-III, the molecular mass of which was higher than STBP-I and -II. In addition, it was demonstrated that small and large STBPs were contained in the seeds at 5 weeks, and STBP-I, -II and -III were contained in the seeds at 6 weeks. On the other hand, Southern blot analysis of digested genomic DNAs from sesame leaves with an STBP cDNA probe indicated the presence of only one copy of STBP in the sesame genome. These results suggested that STBP-III was first produced from a large proprotein precursor in developing sesame seeds, and STBP-I and -II were produced from the same polypeptide chain by different types of post-translational processing.