Molecular mechanisms of generation of pleiotropic effects of recombination genes

重组功能是修复DNA断裂、克服DNA损伤处的DNA复制停滞和维持端粒长度所必需的。我们感兴趣的是如何通过一个单一的重组蛋白产生多种功能。我们选择了Mre 11/rad 50/Xrs 2复合物（MRX）、Rad 51和Rad 52为代表，探讨了它们发挥多功能能力的机制。本研究取得的主要结果如下：（1）Xrs 2与Mre 11结合，并将Mre 11转运到细胞核内，其C-末端有一个由32个氨基酸组成的结构域（MBX）。（2）当Mre 11进入细胞核后，DNA损伤修复不再需要Xrs 2。（3）端粒延长和减数分裂重组除了需要MBX外，还需要其C端104和N端49个氨基酸的结构域：1.我们发现了一条新的检测点通路Te 11-Mre 11，它对DNA双链断裂（DSB）具有特异性。MRX对DSB起传感器作用，激活DSB通路，并在激活通路的引导下进行重组。II.首次发现在DNA同源性搜索中不仅需要rad 51，而且需要rad 52。Rad 51-Rad 52-单链DNA复合体是完成这一过程的复合体，Rad 52在重组的最后阶段，即最终重组分子的产生中也是必需的。由于在该突变体中减数分裂交换的频率特异性降低，因此重组类型、交换类型或基因转换类型的确定可能在重组中间体形成过程中进行，而不是在假定的重组中间体的解析阶段进行。

A recombination function is required for repair of DNA breakages, overcome of DNA replication-arrest at a DNA lesion and maintenance of telomere length. We are interested in how multiple functions are produced by a single recombination protein. We selected a Mre11/rad50/Xrs2 complex (MRX), Rad51 and Rad52 as representatives, and investigated mechanisms that give full play to their multiple functioning ability. The followings are main results obtained during this research term.We analyzed domains of Xrs2 which control the functions of MRX, and found (1)Xrs2 binds to Mre11 with a 32 amino-acid domain (MBX) near the C-terminus, and transports Mre11 into the nucleus. (2)Xrs2 is no more required for DNA damage repair if Mre11 has been transported into the nucleus. (3)For telomere elongation and meiotic recombination, in addition to the MBX, its C-terminal adjacent 104, and its N-terminal adjacent 49-, amino-acid domain are needed, respectively.I.We found a new checkpoint pathway, Te11-Mre11, that is specific to DNA double-strand breakage (DSB), In mitotic cells, Rad53 and Rad9 and in meiotic cells, Mre4/Mek1, are required, respectively. The MRX plays a sensor against the DSB, activates the pathway, and proceeds recombination under the guidance of the activated pathway.II.It is a new finding that not only rad51but also rad52 are necessary for DNA homology search. Rad51-Rad52-single-stranded DNA is the complex to do it. Rad52 is also required at the latest stage of recombination, production of a final recombinant molecule.III.A new helicase gene MER3 was found which is specific to meiotic recombination. As a frequency of meiotic crossover specifically decreases in this mutant, determination of recombinant type, crossover type or gene conversion type, is probably carried out during a process of formation of recombination intermediate, not at the resolution stage of the recombination intermediate as assumed.