Methionine induces sexual development in the fission yeast Schizosaccharomyces pombe via an ste11-dependent signalling pathway.

Methionine added to minimal medium overcomes the repressing effects of ammonium and cyclic AMP (cAMP) on sexual development and efficiently induces mating and sporulation in homothallic strains of Schizosaccharomyces pombe. In heterothallic strains it induces G1 arrest when cells enter stationary phase. We show that methionine reduces the intracellular cAMP pool and induces the expression of at least two cAMP-repressible genes, including fbp1 and ste11. The easiest interpretation of the results is that methionine induces sexual development via a cAMP-dependent ste11 signalling pathway.

Amiloride toxicity in the fission yeast Schizosaccharomyces pombe is released by thiamine and mutations in the thiamine-repressible gene car1.

Amiloride (Am) inhibits growth in the fission yeast Schizosaccharomyces pombe. We show that the toxic effect of this drug is relieved by low concentrations of thiamine (Th) and that the pyrimidine moiety of the Th molecule is responsible for growth inhibition release. A putative membrane protein encoded by the car1 gene is the target for Am action. It is responsible for Am sensitivity and is involved in the utilization of Th and its biosynthetic precursor, 4-amino-5-hydroxymethyl-2-methylpyrimidine. Its expression is repressed by Th and is under the genetic control of the genes, thi1, tnr1, tnr2 and tnr3, which have previously been shown to be responsible for the transcriptional control of genes involved in the biosynthesis and dephosphorylation of Th.

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 as a negative regulator of genes involved in thiamine metabolism (Schweingruber, A. M., Frankhauser, H., Dlugonski, J., Steinmann-Loss, C., and 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 diphosphate, show impaired TPK activity, which is enhanced by introducing the tnr3 wild type gene on a plasmid, and can be complemented by the S. cerevisiae TPK-encoding gene TH180. These data strongly suggest that tnr3 encodes S. pombe TPK. We present evidence that TPK also acts as a negative regulator for gene pho1, which is derepressed when cells are starved for phosphate and show that in contrast to wild type cells, tnr3 mutants mate constitutively in response to thiamine, indicating that TPK is also involved in regulation of mating. Disruption of the tnr3 gene is lethal, and a tnr3 mutant expressing only residual TPK activity grows slowly and shows aberrant morphology.

Growth of a mutant defective in a putative phosphoinositide-specific phospholipase C of Schizosaccharomyces pombe is restored by low concentrations of phosphate and inositol.

A mutant (plc1-1) of Schizosaccharomyces pombe unable to grow on a minimal medium containing high amounts of phosphate was selected. On yeast-extract agar its growth is temperature sensitive. Tests in liquid synthetic medium show that growth of the mutant is partially restored by lowering the phosphate and inositol concentrations in the growth medium. The growth defect is fully suppressed by a plasmid encoding a putative protein having the structural features of phosphoinositide-specific phospholipases C (PI-PLC). This protein, of 899 amino-acids, contains the characteristic X and Y domains found in all PI-PLCs of higher and lower eucaryotes and reveals, in addition, an EF-hand motif (putative Ca(2+)-binding site). Like the corresponding enzyme from Saccharomyces cerevisiae, the S. pombe PI-PLC is most similar to the delta form of PI-PLC isoenzymes. The cloned gene integrates at the plc1 site indicating that plc1 codes for a putative PI-PLC. Plc1 physically maps on the left arm of chromosome II between rad11 and mei3.

Regulation of pho1-encoded acid phosphatase of Schizosaccharomyces pombe by adenine and phosphate.

Expression of pho1-encoded acid phosphatase of Schizosaccharomyces pombe has been reported to be regulated by phosphate. In this communication we show that it is also regulated by adenine. Starving adenine auxotrophic strains for adenine leads to a drastic increase of the enzymatic activity while adenine represses this activity. Full repression by adenine only occurs when phosphate is not growth limiting and vice versa. Regulation occurs at the level of mRNA. We isolated adenine non-repressible mutants. They define four genes (anr1, anr2, anr3, and anr5) which are involved in adenine-dependent pho1 expression. All anr mutants are also phosphate non-repressible. These results indicate that the generation and/or transduction of the intracellular signal responsible for pho1 repression is simultaneously dependent on both adenine and phosphate.

Thiamine in Schizosaccharomyces pombe: dephosphorylation, intracellular pool, biosynthesis and transport.

We have investigated the thiamine metabolism in Schizosaccharomyces pombe and shown that: (1) Thiamine-repressible acid phosphate, coded for by the gene pho4, dephosphorylates thiamine phosphates indicating that the enzyme acts as a thiamine phosphate phosphatase. (2) In vivo synthesized thiamine is present intracellularly mainly as thiamine diphosphate. Starving cells for glucose decreases the intracellular thiamine pool. (3) The genes thi2, thi3 and thi4 control thiamine biosynthesis and probably code for thiamine biosynthetic enzymes. Thi3, which is involved in the synthesis of the pyrimidine moiety of the thiamine molecule, is allelic to the thiamine repressible gene nmt1. (4) Thiamine uptake is a thiamine regulated process, probably occurs by active transport and is controlled by the gene ptr1.

Thiamin regulates agglutination and zygote formation in Schizosaccharomyces pombe.

Nutritional conditions regulate mating of the fission yeast S. pombe. To investigate how nutritional signals are monitored by the cell and translated into appropriate mating behaviour, effects of unique and specific growth factors would be desirable. We show that thiamin can inhibit sexual agglutination and zygote formation in S. pombe. A concentration of 50 nM thiamin in the culture medium is required for full growth of a thiamin auxotrophic strain. At this concentration thiamin starts to inhibit mating of wild-type cells of opposite heterothallic mating type and at a 1 microM concentration zygote formation is inhibited by more than 95%. Growth conditions modulate the inhibitory effect of thiamin. Thiamin acts only for a restricted period of time and seems to inhibit commitment to zygote formation rather than the cell aggregation and fusion process itself. Pyrithiamin, a thiamin antagonist, inhibits growth as well as mating.