| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
Chromosomal DNA is exposed to various DNA-damaging agents and sustains damage that induces genomic instability. A double-strand break (DSB) is caused by ionizing radiation, crosslinking reagents, oxidative stress, and DNA replication failure. If the DSB is left unrepaired, then cell death occurs. Homologous recombination is one of the major DSB repair pathways. This repair pathway is essentially error-free, since a homologous region of the undamaged sister chromatid is used as the template for repair. In contrast to the mitotic DSB repair pathway, meiotic cell division involves homologous recombination between homologous chromosomes, but not between sister chromatids. This preferential recombination between homologous chromosomes is initiated by the formation of a programmed double strand break (DSB), and ensures correct chromosomal segregation at meiosis I through the formation of chiasmata, which physically connect homologous chromosomes. Thus, homologous recombination is important to maintain the integrity of the chromosome in both mitotic and meiotic cells.
In homologous recombination, a single-stranded DNA (ssDNA) tail, produced at the DSB site, is incorporated into a nucleoprotein complex called the presynaptic filament. This presynaptic filament catalyzes homologous pairing and strand exchange with an intact homologous region of the double-stranded DNA (dsDNA) molecule. The bacterial RecA protein is known to form helical presynaptic filaments and to play central roles in homologous recombination. In eukaryotes, two homologs of RecA, the Rad51 and Dmcl proteins, which are conserved from yeast to human, are assumed to fulfill this role.
We have determined the crystal structure of the human Dmcl protein as an octameric ring form. Then, we performed the structure-based mutation analyses of the Rad51 and Dmcl proteins, and identified residues that function in DNA-binding and octameric ring formation.
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