Isolation and analysis of yeast genes involved in meiotic first division

我们研究了负责裂殖酵母减数分裂第一次分裂的基因。突变株J13的分离及遗传分析该突变株是通过甲烷磺酸盐诱变获得的，在减数分裂前期停滞的冷敏突变株J13。该突变体命名为J13，在18ﾟC时不能完成减数分裂I，但在30ﾟC时形成正常的4孢子Asci。遗传分析表明，J13含有一个单隐性突变，并定义了一个新的遗传位点mei10。Mei10基因定位于第二染色体着丝粒附近。Mei4基因的结构与表达克隆了含有mei4基因的2.8kb DNA片段，并测定了其核苷酸序列。发现了由356个密码子组成的开放阅读框架。预测的mei4基因产物大小为39 kDa，具有亲水性，富含丝氨酸残基。在氨基酸序列上没有已知的与mei4蛋白相似的蛋白质。Northern分析表明，mei4基因在无氮条件下优先转录。Mei4的这种转录激活既不需要交配型基因的杂合性，也不需要mei2基因的功能，后者是启动减数分裂的先决条件。

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.