title: Homologous-pairing activity of the human DNA-repair proteins Xrcc3.Rad51C.
abstract: The human Xrcc3 protein is involved in the repair of damaged DNA through homologous recombination, in which homologous pairing is a key step. The Rad51 protein is believed to be the only protein factor that promotes homologous pairing in recombinational DNA repair in mitotic cells. In the brain, however, Rad51 expression is extremely low, whereas XRCC3, a human homologue of Saccharomyces cerevisiae RAD57 that activates the Rad51-dependent homologous pairing with the yeast Rad55 protein, is expressed. In this study, a two-hybrid analysis conducted with the use of a human brain cDNA library revealed that the major Xrcc3-interacting protein is a Rad51 paralog, Rad51C/Rad51L2. The purified Xrcc3.Rad51C complex, which shows apparent 1:1 stoichiometry, was found to catalyze the homologous pairing. Although the activity is reduced, the Rad51C protein alone also catalyzed homologous pairing, suggesting that Rad51C is a catalytic subunit for homologous pairing. The DNA-binding activity of Xrcc3.Rad51C was drastically decreased in the absence of Xrcc3, indicating that Xrcc3 is important for the DNA binding of Xrcc3.Rad51C. Electron microscopic observations revealed that Xrcc3.Rad51C and Rad51C formed similar filamentous structures with circular single-stranded DNA.
authors.affiliation: Genomic Sciences Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama-shi, Kanagawa 230-0045, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kurumizaka
authors.forename: S
authors.initials: S
authors.lastname: Ikawa
authors.forename: M
authors.initials: M
authors.lastname: Nakada
authors.forename: K
authors.initials: K
authors.lastname: Eda
authors.forename: W
authors.initials: W
authors.lastname: Kagawa
authors.forename: M
authors.initials: M
authors.lastname: Takata
authors.forename: S
authors.initials: S
authors.lastname: Takeda
authors.forename: S
authors.initials: S
authors.lastname: Yokoyama
authors.forename: T
authors.initials: T
authors.lastname: Shibata
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D051135:Rad51 Recombinase; D020798:Two-Hybrid System Techniques
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; C110901:X-ray repair cross complementing protein 3; D051135:Rad51 Recombinase