Incorporation of histidine into the pyrimidine moiety of thiamin in Saccharomyces cerevisiae.

To investigate the incorporation of histidine into the pyrimidine moiety of thiamin in eukaryotes, Saccharomyces cerevisiae was grown in a synthetic medium in the presence of 15N- or 14C-labeled histidine. Two 15N-atoms of DL-[1,3-15N2]histidine were incorporated into the N-3 and amino-N atom at C-4 of pyrimidine. Furthermore, incorporation of the 15N-amino group of aspartate, the origin of the N-1 of histidine, into the N-3 of pyrimidine shows that N-3 and the amino-N atom at C-4 of pyrimidine are derived from N-1 and N-3 of histidine, respectively. In contrast, the 15N atom of DL-[amino-15N]histidine was not incorporated into the molecule, whereas L-[2-14C]histidine was incorporated directly into the pyrimidine. We conclude that N-1, C-2, and N-3 of histidine are the origins of the N-3, C-4, and amino-N at C-4 of the pyrimidine in thiamin synthesized by S. cerevisiae.