| Research Abstract |
Homologous DNA paring is the formation of a heteroduplex joint, which is intermolecular double-stranded DNA between single-stranded DNA and the complementary strand of homologous intact double-stranded DNA in homologous recombination-DNA repair. Single-stranded DNA is derived from a DNA double-stranded break or a single-stranded gap, in vivo. Heteroduplex joints are general intermediates in homologous DNA recombination. It has been generally believed that homologous DNA pairing is catalyzed by an ATP-dependent activity of RecA-family proteins, such as RecA, Rad51 and Dmc1. We had found a group of proteins that catalyze homologous DNA pairing in the absence of ATP (non-RecA proteins ; e.g., Rad52, Mhr1) and their novel functions in genetic inheritance including mitochondrial DNA-homoplasmy. We studied to elucidate the basic principles governing homologous recombination by comparative analyses of homologous pairing by RecA-family proteins and that by non-RecA-proteins. We investigated RecA of Escherichia coli and Thermus thermophilus as RecA-family proteins, and Mhr1 of Saccharomyces cerevisiae mitochondria and RecO of Thermus thermophilus as non-RecA proteins. We carried out NMR-analyses, and molecular genetic and biochemical analyses including site-directed mutagenesis. The major outcome of this study is as follows : the NMR-analysis supports the conclusion that RecA-family proteins and non-RecA proteins catalyze homologous DNA pairing through a common mechanism; i.e., the mechanism includes an extended DNA intermediate stabilized by a CH-pi interaction between 2' methylene moiety of deoxyribose and the base of the following nucleotide residue (Nishinaka, T., Ito, Y., Yokoyama, S. and Shibata, T. : Proc.Natl.Acad.Sci. USA, 94, 6623 (1997) ; Nishinaka, T., Shinohara, A., Ito, Y., Yokoyama, S. and Shibata, T. : Proc.Natl.Acad.Sci. USA, 95, 11071 (1998)).
|
