Ogawa H, Johzuka K, Nakagawa T, Leem S H, Hagihara A H
Department of Biology, Faculty of Science, Osaka University, Japan.
Adv Biophys. 1995;31:67-76. doi: 10.1016/0065-227x(95)99383-z.
Mutants defective in meiotic recombination were isolated using a disomic haploid strain of S. cerevisiae, and were classified into 11 genes. Two, MRE2 and MRE11, are new genes and nine are previously identified genes. The mre2 and mre11 deletion mutants are proficient in mitotic recombination, but are defective in meiotic recombination and in formation of viable spores. The spore inviability, however, is alleviated by an additional mutation, spo13, which bypasses meiosis I. In addition, neither meiosis specific DSBs at recombination hot-spots nor formation of synaptonemal complex occur in either mutant. Therefore, these two genes are involved in the formation of DSBs in meiotic recombination. While a temperature sensitive mre11-1 mutant is able to form DSBs at a permissive temperature, the formed DSBs are unable to resect at non permissive temperature. Therefore, the MRE11 gene is also involved in some step of the repair process after the DSB formation. Analysis of properties of the mre11 disruption mutant as well as the xrs2 mutant showed a similarity to those of the rad50 disruptant. We found that the mre11 disruption mutation is epistatic to rad50S mutation, as the xrs2 deletion mutation is epistatic to rad50S with regard to DSBs. Therefore, these three genes form an epistatic group. Interaction of the Mre11 protein with the Rad50 and the Xrs2 protein as well as alone was shown in vivo using the two-hybrid system. The MRE2 gene encodes a protein containing two sets of RRM. Deficiency of recombination in a mre2 mutant that has an amino acid substitution in the N-terminal RRM can be suppressed by the MER2 gene on the multicopy plasmid. Further analysis showed that the Mre2 protein is involved in meiosis-specific splicing of the MER2 transcripts in cooperation with the Mer1 protein. In conclusion, MRE genes are involved in the initiation of meiotic recombination through the formation of DSBs at recombination hot-spots in S. cerevisiae.
利用酿酒酵母的二体单倍体菌株分离出减数分裂重组缺陷型突变体，并将其分为11个基因。其中两个，MRE2和MRE11，是新基因，九个是先前已鉴定的基因。mre2和mre11缺失突变体在有丝分裂重组方面表现正常，但在减数分裂重组和形成有活力的孢子方面存在缺陷。然而，通过额外的突变spo13可以缓解孢子的无活力，spo13可绕过减数分裂I。此外，在这两种突变体中，减数分裂特异性的双链断裂（DSB）在重组热点处均未发生，也未形成联会复合体。因此，这两个基因参与减数分裂重组中DSB的形成。虽然温度敏感型mre11 - 1突变体在允许温度下能够形成DSB，但在非允许温度下形成的DSB无法进行切除。因此，MRE11基因也参与DSB形成后的修复过程的某些步骤。对mre11破坏突变体以及xrs2突变体的特性分析表明，它们与rad50破坏突变体相似。我们发现mre11破坏突变对rad50S突变是上位性的，就像xrs2缺失突变在DSB方面对rad50S是上位性的一样。因此，这三个基因形成一个上位性组。利用双杂交系统在体内显示了Mre11蛋白与Rad50和Xrs2蛋白以及单独的Mre11蛋白之间的相互作用。MRE2基因编码一种含有两组RRM的蛋白质。在N端RRM中具有氨基酸替换的mre2突变体中，重组缺陷可被多拷贝质粒上的MER2基因抑制。进一步分析表明，Mre2蛋白与Mer1蛋白协同参与MER2转录本的减数分裂特异性剪接。总之，MRE基因通过在酿酒酵母的重组热点处形成DSB参与减数分裂重组的起始。
