Molecular mechanisms of generation of pleiotropic effects of recombination genes

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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.