Fission yeast Tor1 functions in response to various stresses including nitrogen starvation, high osmolarity, and high temperature

A target of rapamycin (TOR) protein is a protein kinase that exerts cellula r signal transduction to regulate cell growth in response to extracellular nutrient conditions. In the Schizosaccharomyces pombe genome database, ther e are two genes encoding TOR-related proteins, but their functions have not been analyzed. Here we report that one of the genes, referred to as tor1(), is required for sexual development induced by nitrogen starvation. Ste11 is a key transcription factor for the initiation of sexual development. Th e expression of ste11(+) is normally regulated in tor1(-) cells; and overex pression of ste11(+) hardly rescues the defect in fertility in tor1(-). Upo n nitrogen starvation, tor1(+) cells promote two rounds of the cell cycle t o become arrested at the G1 phase before initiation of sexual development. The tor1(-) cells do not promote such a cell cycle, suggesting that Tor1 is necessary for the response to nitrogen starvation, The tor1(-) cells show no growth or very slow growth under various stress conditions, including ex ternal high pH, high concentrations of salts or sorbitol, and high temperat ure. These results suggest that Tor1 is necessary for any response to a wid e range of stresses. The vegetative growth of tor1(-) cells is inhibited by rapamycin, although tor1(+) cells are resistant to the drug. The tor1(-) c ells are hypersensitive to fluphenazine and cyclosporin A, which specifical ly inhibit calmodulin and calcineurin respectively.