SCHIZOSACCHAROMYCES-POMBE THIAMINE PYROPHOSPHOKINASE IS ENCODED BY GENE TNR3 AND IS A REGULATOR OF THIAMINE METABOLISM, PHOSPHATE-METABOLISM, MATING, AND GROWTH

The Schizosaccharomyces pombe gene tnr3 has been genetically defined a s a negative regulator of genes involved in thiamine metabolism (Schwe ingruber, A. M., Fankhauser, H., Dlugonski, J., Steinmann-Loss, C., an d Schweingruber, M. E. (1992) Genetics 130, 445-449). We have isolated and sequenced the gene and show that it codes for a putative protein of 569 amino acids which exhibits, in its carboxyl-terminal half, good homology to Saccharomyces cerevisiae thiamine pyrophosphokinase (TPK) . tnr3 mutants have reduced levels of intracellular thiamine diphospha te, show impaired TPK activity, which is enhanced by introducing the t nr3 wild type gene on a plasmid, and can be complemented by the S. cer evisiae TPK-encoding gene TH180. These data strongly suggest that tnr3 encodes S. pombe TPK. We present evidence that TPK also acts as a neg ative regulator for gene pho1, which is derepressed when cells are sta rved for phosphate and show that in contrast to wild type cells, tnr3 mutants mate constitutively in response to thiamine, indicating that T PK is also involved in regulation of mating. Disruption of the tnr3 ge ne is lethal, and a tnr3 mutant expressing only residual TPK activity grows slowly and shows aberrant morphology.