Rockmill B, Engebrecht J A, Scherthan H, Loidl J, Roeder G S
Department of Biology, Yale University, New Haven, Connecticut 06520-8103, USA.
Genetics. 1995 Sep;141(1):49-59. doi: 10.1093/genetics/141.1.49.
Mutation of the MER2 gene of Saccharomyces cerevisiae confers meiotic lethality. To gain insight into the function of the Mer2 protein, we have carried out a detailed characterization of the mer2 null mutant. Genetic analysis indicates that mer2 completely eliminates meiotic interchromosomal gene conversion and crossing over. In addition, mer2 abolishes intrachromosomal meiotic recombination, both in the ribosomal DNA array and in an artificial duplication. The results of a physical assay demonstrate that the mer2 mutation prevents the formation of meiosis-specific, double-strand breaks, indicating that the Mer2 protein acts at or before the initiation of meiotic recombination. Electron microscopic analysis reveals that the mer2 mutant makes axial elements, which are precursors to the synaptonemal complex, but homologous chromosomes fail to synapse. Fluorescence in situ hybridization of chromosome-specific DNA probes to spread meiotic chromosomes demonstrates that homolog alignment is also significantly reduced in the mer2 mutant. Although the MER2 gene is transcribed during vegetative growth, deletion or overexpression of the MER2 gene has no apparent effect on mitotic recombination or DNA damage repair. We suggest that the primary defect in the mer2 mutant is in the initiation of meiotic genetic exchange.
酿酒酵母MER2基因的突变会导致减数分裂致死。为深入了解Mer2蛋白的功能，我们对mer2基因敲除突变体进行了详细的特性分析。遗传分析表明，mer2完全消除了减数分裂染色体间基因转换和交叉互换。此外，mer2还消除了核糖体DNA阵列和人工重复序列中的染色体内减数分裂重组。物理检测结果表明，mer2突变阻止了减数分裂特异性双链断裂的形成，这表明Mer2蛋白在减数分裂重组起始时或之前发挥作用。电子显微镜分析显示，mer2突变体形成了轴元件，轴元件是联会复合体的前体，但同源染色体无法联会。用染色体特异性DNA探针与铺展的减数分裂染色体进行荧光原位杂交表明，mer2突变体中同源染色体的配对也显著减少。尽管MER2基因在营养生长期间转录，但MER2基因的缺失或过表达对有丝分裂重组或DNA损伤修复没有明显影响。我们认为，mer2突变体的主要缺陷在于减数分裂遗传交换的起始。
