Molecular mechanism of meiotic recombination

酵母中的遗传重组，S。酿酒酵母减数分裂比有丝分裂约1000倍。这种减数分裂重组的增加是由联会复合体（SC）和重组结节的形成提供的。为了阐明这些结构复合物在减数分裂重组中的作用，我们试图分离参与这些复合物形成的突变体。作为候选突变体，我们分离到了新的突变体mre 2、mre 3、mre 11，这些突变体在有丝分裂重组中表现出优势，但在减数分裂重组中表现出缺陷。对这些突变体的性质的分析显示了以下结果。当编码携带RNA结合蛋白的共有氨基酸序列的蛋白质的MRE 2基因有缺陷时，观察到未配对染色体（即轴向元件）的形成，但没有观察到联会复合体。此外，在该突变体中，减数分裂第一次分裂比野生型早1小时开始，但减数分裂第二次分裂在正常时间开始， ...更多信息 g减数分裂开始后。在第一次分裂中，突变体纺锤体极体的分离距离比野生型增加了2倍。通过测量一对分开的主轴极体之间的管线长度证实了这一观察结果。这些结果表明，MRE 2参与配对的同源染色体，也在减数分裂的第一次分裂的开始，同时。MRE 3基因通过合成起始位点不同的两种mRNA来表达两种不同的蛋白质。一个在有丝分裂中合成，覆盖MRE 3基因的整个ORF。而另一个则在减数分裂中特异性合成，并从ORF的近端开始合成。前者的功能是有丝分裂生长所必需的，而另一个蛋白的功能是减数分裂重组所必需的。在该基因的完全缺失突变体中，没有观察到轴向元件（SC的前体）的形成。MRE 11基因对RAD 50基因具有上位性，不仅参与减数分裂特异性双链断裂（DSB）在重组热点的引入，而且同时参与DSB的加工。少

Genetic recombination in yeast, S. cerevisiae, ocurs about 1000 times in meiosis than in mitosis. This increment in meiotic recombination is provided by the formation of the synaptonemal complex (SC) and recombination nodule. To clarify the roles of these structural complexes in meiotic recombination, we attempted to isolate the mutants involved in the formation of these complexes. As the candidates, we isolated new mutants, mre2, mre3, mre11, that area proficient in mitotic recombination but defective in meiotic recombination. Analysis of the properties of these mutants showed the following results. When the MRE2 gene, which encodes a protein carrying a consensus amino acid sequence for RNA binding proteins, is defective, the formation of the unpaired chromosomes, that is, axial elements, were observed but not the synaptonemal complex. Moreover, in this mutant the meiotic first division starts one hour earlier than in wild type, but the meiotic second division starts at a normal timin … More g after the onset of the meiosis. During the first division in the mutant, distance of the separated spindle pole body increased two times of that in wild type. This observation was confirmed by the measuring the lengths of the tublines between a pair of the divided spindle pole bodies. These results suggest that the MRE2 is involved in the pairing of the homologous chromosomes and also in the onset of the meiotic first division, simultaneously. The MRE3 gene expresses two different proteins by synthesizing two kinds of mRNA differing in the starting sites. One is synthesized in mitosis and covered the whole ORF of the MRE3 gene. While, the another is synthesized in meiosis specifically and starts form the proximal part within the ORF. The function of the former protein is required for the mitotic growth and that of the another for meiotic recombination. In the complete deletion mutant of this gene, the formation of the axial elements, precursors of the SC, was not observed. The MRE11 is found to be epistatic to the RAD50 gene and is involved in not only the introduction of the meiosis specific double strand breaks (DSBs) at the recombination hot spots but also the processing of the DSBs simultaneously. Less