サッカロミセス酵母における性及び種の分化
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概要
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We isolated heterothallic haploid strains from a homothallic diploid strain of a yeast Saccharomyces exiguus by mutagenization with UV or ethylmethanesulfonate(EMS). A gene, not linked to the mating-type locus, was found to control homothallism in the yeast, as in Saccharomyces cerevisiae. In heterothallic strains of S. exiguus, sexual agglutination followed by zygote formation was observed when a-type and α-type haploid strains were mixed. This mating process was regulated by mating pheromones secreted by both type cells. Neither sexual agglutination nor zygote formation occurred between 5. exiguus and S. cerevisiae or Saccharomyces kluyveri. a Pheromone of 5. exiguus acted only on α type cells of S. exiguus. On the contrary, α pheromone of S. exiguus induced sexual agglutination of an inducible a-type cells of S. cerevisiae. We purifyed α pheromone of S. exiguus and determined its ammo acid sequence, α Pheromone of S. exiguus is a linear tridecapeptide whose sequence slightly differed from those of S. cerevisiae and S. kluyveri. These α pheromones from S. cerevisiae, S. kluyveri and S. exiguus displayed interspecific actions on the a-type cells of all three yeast species. The intraspecific α pheromone-a-type cell reaction was not necessarily more effective than the interspecific one. Finally, the DNA of S. exiguus was analyzed by Southern hybridization using the cloned MATa, MATα and HO genes of S. cerevisiae as probes. It was shown that S. exiguus has a DNA sequence homologous with the HO gene of S. cerevisiae. Pulsed field gel electrophoresis revealed that this DNA sequence located on a chromosome of about 940Kb of DNA in S. exiguus. However, no DNA sequence homologous with the MAT genes of S. cerevisiae was detected in S. exiguus.