title: Sister chromatid exchanges are mediated by homologous recombination in vertebrate cells.
abstract: Sister chromatid exchange (SCE) frequency is a commonly used index of chromosomal stability in response to environmental or genetic mutagens. However, the mechanism generating cytologically detectable SCEs and, therefore, their prognostic value for chromosomal stability in mitotic cells remain unclear. We examined the role of the highly conserved homologous recombination (HR) pathway in SCE by measuring SCE levels in HR-defective vertebrate cells. Spontaneous and mitomycin C-induced SCE levels were significantly reduced for chicken DT40 B cells lacking the key HR genes RAD51 and RAD54 but not for nonhomologous DNA end-joining (NHEJ)-defective KU70(-/-) cells. As measured by targeted integration efficiency, reconstitution of HR activity by expression of a human RAD51 transgene restored SCE levels to normal, confirming that HR is the mechanism responsible for SCE. Our findings show that HR uses the nascent sister chromatid to repair potentially lethal DNA lesions accompanying replication, which might explain the lethality or tumorigenic potential associated with defects in HR or HR-associated proteins.
authors.affiliation: Bayer-Chair Department of Molecular Immunology and Allergology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors.forename: E
authors.initials: E
authors.lastname: Sonoda
authors.forename: M S
authors.initials: MS
authors.lastname: Sasaki
authors.forename: C
authors.initials: C
authors.lastname: Morrison
authors.forename: Y
authors.initials: Y
authors.lastname: Yamaguchi-Iwai
authors.forename: M
authors.initials: M
authors.lastname: Takata
authors.forename: S
authors.initials: S
authors.lastname: Takeda
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear; D030161:Avian Proteins; D002645:Chickens; D004265:DNA Helicases; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics; D006801:Humans; D000072200:Ku Autoantigen; D009687:Nuclear Proteins / Q000235:genetics; D051135:Rad51 Recombinase; D012854:Sister Chromatid Exchange
chemical_list: D034961:Antigens, Nuclear; D030161:Avian Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C495150:RAD51 protein, Gallus gallus; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D004265:DNA Helicases; C103532:RAD54L protein, human; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen