Speciation mochauism of hemiascamycetans yeasts

为了阐明与性相互作用有关的基因多样性对物种形成机制的影响，笔者对酿酒酵母（Saccharomyces cerevisiae）和长石酵母（Saccharomyces naganishii）的性别分化基因进行了比较研究。S. naganishii是我们通过对酵母菌分子分类学的重新研究发现的一个新种，具有高度产孢能力，具有完善的ho型同殖性。我已经从原长石链球菌的同型菌株中分离出异型菌株。我构建了一个宿主载体系统专门针对长石氏。所构建的载体具有一个自主复制序列和一个来源于长石线虫染色体的着丝粒序列。然后，我利用上述高度稳定的ycp型载体构建了S. naganishii基因组文库。我从文库中克隆出了长石链球菌α信息素的编码基因，并与酿酒链球菌的α信息素基因进行了比较。长石链球菌的α信息素前体与酿酒链球菌的α信息素前体非常接近。然后，我试图绘制两种物种α信息素基因上游调控序列（URSs）的差异。从LacZ报告基因的表达来看，长石螺α信息素基因URS在两种物种的α型细胞中都被激活。当从URS中省略了一个被预测为在S. naganishii中激活该基因所必需的区域时，LacZ报告基因在S. naganishii中完全不表达，但在S. cerevisiae中部分表达。这些结果表明，两种植物的交配型基因产物将不同的序列识别为功能性URSs。

In order to clarify the effect of gene diversity concerned with sexual interactions on speciation mechanism, I tried to perform comparative study of sex-differentiation genes between the yeasts Saccharomyces cerevisiae and Saccharomyces naganishii. S. naganishii is a new species described by us through the molecular taxonomic reexamination of Saccharomyces yeasts, has the ability to highly sporulate, and has a perfect Ho-type homothallism. I have already isolated heterothallic strains from the original homothallic strain of S. naganishii.I constructed a host-vector system specific to S. naganishii. The vector constructed has an autonomously replicating sequence and a centromere sequence derived from S. naganishii chromosome. Then, I constructed a genomic library of S. naganishii with the above highly stable YCp-type vector. From the library, I cloned a gene coding for alpha pheromone of S. naganishii, and compare it with the one of S. cerevisiae. A precursor of alpha pheromone of S. naganishii is very close to the one of S. cerevisiae. Then, I tried to draw difference of upstream regulatory sequences (URSs) of alpha pheromone genes between the two species. The URS of alpha pheromone gene from S. naganishii was activated in alpha-type cells of both species, in terms of LacZ reporter gene expression. When a region predicted to be essential to activate the gene in S. naganishii was omitted from the URS, LacZ reporter gene was not expressed at all in S. naganishii, but was partially expressed in S. cerevisiae. These results suggested that products of mating-type genes from the two species recognize different sequences as functional URSs.