| Budget Amount *help |
¥6,700,000 (Direct Cost: ¥6,700,000)
Fiscal Year 1986: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1985: ¥5,500,000 (Direct Cost: ¥5,500,000)
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| Research Abstract |
The fission yeast Schizosaccharomyces pombe changes its cellular activity dramatically towards meiosis under certain conditions. Our molecular genetic studies of the mechanism which triggers meiosis in this yeast resulted in the following findings. 1. Once transferred to the restrictive temperature, the pat1 mutants of S. pombe, which we isolated, halt growth and initiate meiosis disregarding prerequisites (nutrition and mating type) normally required for meiosis. We could demonstrate that the meiotic pathway which these mutants follow is essentially identical to the natural one. Thus, the pat1 gene apparently encodes a negative control element which represses the initiation reaction for meiosis during vegetative growth. We also found that pat1 is completely suppressed if the mei2 gene is defective. We suspect that mei2 encodes a crucial positive factor involved in the initiation reaction of meiosis. 2. We determined the complete nucleotide sequence of mei2 and found an ORF of 750 amin
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o acids. Transcription of mei2 was markedly induced if nitrogen is depleted from media, although this induction is seen both in sporogenic and asporogenic cells. We identified four initiation sites for transcription of the mei2 gene. 3. We isolated another pat1 suppressor, steX, in addition to mei2. Strains defective in steX are deficient in mating as well as in meiosis. 4. We isolated S. pombe mutants insensitive to cAMP, which inhibits meiosis in this yeast, and classified them into four groups (cai1 - 4). Products of these genes are likely to mediate the effect of cAMP as a member of the cAMP cascade. 5. We constructed strains carrying disrupted ras1, a ras oncogene homolog in S. pombe. They are completely incapable of mating, can enter meiosis only inefficiently, but are not defective in vegetative growth. Their sterility was ascribed to their defect in recognition of a mating pheromone-like diffusible factor released by S. pombe. 6. We cloned the gene encoding calmodulin in S. pombe (cam1) and disrupted it. Results indicate that calmodulin is essential for vegetative growth and that its intracellular amount is not in excess. Less
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