Isolation and analysis of yeast genes involved in meiotic first division

我们研究了裂糖酵母（Schizosaccharomyces pombe）中负责减数分裂第一次分裂的基因。突变体J13的分离与遗传分析利用甲烷磺酸乙酯诱变方法，从pombe S. homthallic菌株中获得了减数分裂I前期捕获的冷敏感突变体。该突变体命名为J13，在18ºC时不能完成减数分裂I，但在30ºC时形成正常的4孢子asci。遗传分析表明，J13携带一个单隐性突变，并定义了一个新的遗传位点mei10。mei10基因定位在第II.2号染色体的着丝粒附近。克隆了含有mei4基因的2.8kb DNA片段，并测定了其核苷酸序列。发现356个密码子组成的开放阅读框。这个39 kDa的me4基因产物被认为是亲水的，富含丝氨酸残基。在氨基酸序列上没有已知的与mei4蛋白相似的蛋白。Northern分析表明，mei4基因在无氮培养基下优先转录。这种mei4的转录激活既不需要交配型位点的杂合性，也不需要mei2基因的功能，而这是减数分裂开始的先决条件。

We have studied the genes responsible for the meiotic first division in the fission yeast Schizosaccharomyces pombe.1. Isolation and genetic analysis of the mutant J13 The cold-sensitive mutant which was arrested at the prophase of meiosis I was obtained from an S. pombe homothallic strain by ethylmethane sulfonate mutagenesis. The mutant, named J13, was unable to complete meiosis I at 18ﾟC, but formed normal 4-spored asci at 30ﾟC. Genetic analyses revealed that J13 harbored a single recessive mutation and defined a new genetic locus, mei10. The mei10 gene was mapped in the vicinity of the centromere on chromosome II.2. Structure and expression of the mei4 gene The 2.8kb DNA fragment containing the mei4 gene was cloned and its nucleotide sequence was determined. The open reading frame composed of 356 codons was found. This predicted mei4 gene product of 39 kDa was supposed to be hydrophilic and rich in serine residues. There were no known proteins which resembled the mei4 protein in the amino acid sequence. Northern analysis showed that the mei4 gene was preferentially transcribed under nitrogen- free medium. This transcriptional activation of mei4 required neither the heterozygosity at the mating-type locus nor the mei2 gene function which were known to be prerequisite to the initiation of meiosis.