Study on Genetic Recombination Systems in Eukaryotes

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We set three main subjects as follows. (1) Elucidation of away of recognition in abase sequence between two homologous DNA molecules. (2) Analysis of structures and functions of recombination apparatuses for initiation and formation of recombination intermediates. (3) Analysis of chromosome structures required for recombination process.The following are the prominent results that we obtained for a five-year period of this investigation. (1) Structure of RecA-DNA complexes was analyzed by NMR spectroscopy. Analysis revealed that the DNA structure in the complexes contained novel deoxyribose-base stacking and bases of the single-stranded DNA were spaced out nearly 0.5 run. This novel structure prompted us to propose a new model for a recognition mechanism of homologous base sequence in homologous pairing. (2) We analyzed the function of the Mre 11 protein that played a central role in the initiation of meiotic recombination. The Mre 11 protein was involved in DNA double-strand break (DSB … More ) formation and carried out processing from the DSBs with its nuclease activities. In addition, Mre 11 protein also carried out non-homologous end joining reaction of DSBs and was involved in illegitimate recombination through the reaction. These findings suggest that the Mre 11 protein acts at the junction of homologous recombination pathway and illegitimate recombination pathway and may provide a breakthrough in improving a low frequency of gene targeting in eukaryotic cells. (3) Strand-transfer activity was observed for Rad5l protein at a high level as RecA protein by addition of Rad52 and REP proteins in the reaction mixture. This finding will accelerate the analysis of molecular mechanism of formation of recombination intermediates in eukaryotes.All results obtained contributed directly to the research field with repair of DSBs produced by irradiation of ionizing radiation. Furthermore they proposed new research problems, what a relationship is existed between meiotic recombination and DNA damage check point system, and how the Mre 11 protein is invoked in maintenance of a telomere length or repeated nucleotide sequences. Less