title: Nbs1 is essential for DNA repair by homologous recombination in higher vertebrate cells.
abstract: Double-strand breaks occur during DNA replication and are also induced by ionizing radiation. There are at least two pathways which can repair such breaks: non-homologous end joining and homologous recombination (HR). Although these pathways are essentially independent of one another, it is possible that the proteins Mre11, Rad50 and Xrs2 are involved in both pathways in Saccharomyces cerevisiae. In vertebrate cells, little is known about the exact function of the Mre11-Rad50-Nbs1 complex in the repair of double-strand breaks because Mre11- and Rad50-null mutations are lethal. Here we show that Nbs1 is essential for HR-mediated repair in higher vertebrate cells. The disruption of Nbs1 reduces gene conversion and sister chromatid exchanges, similar to other HR-deficient mutants. In fact, a site-specific double-strand break repair assay showed a notable reduction of HR events following generation of such breaks in Nbs1-disrupted cells. The rare recombinants observed in the Nbs1-disrupted cells were frequently found to have aberrant structures, which possibly arise from unusual crossover events, suggesting that the Nbs1 complex might be required to process recombination intermediates.
authors.affiliation: Department of Environmental Sciences, Faculty of Science, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512 Japan. htauchi@mx.ibaraki.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tauchi
authors.forename: Junya
authors.initials: J
authors.lastname: Kobayashi
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Morishima
authors.forename: Dik C
authors.initials: DC
authors.lastname: van Gent
authors.forename: Takahiro
authors.initials: T
authors.lastname: Shiraishi
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Verkaik
authors.forename: Diana
authors.initials: D
authors.lastname: vanHeems
authors.forename: Emi
authors.initials: E
authors.lastname: Ito
authors.forename: Asako
authors.initials: A
authors.lastname: Nakamura
authors.forename: Eiichiro
authors.initials: E
authors.lastname: Sonoda
authors.forename: Minoru
authors.initials: M
authors.lastname: Takata
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takeda
authors.forename: Shinya
authors.initials: S
authors.lastname: Matsuura
authors.forename: Kenshi
authors.initials: K
authors.lastname: Komatsu
mesh_terms: D000818:Animals; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002645:Chickens; D002869:Chromosome Aberrations / Q000528:radiation effects; D004247:DNA / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage / Q000528:radiation effects; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D005785:Gene Conversion; D017353:Gene Deletion; D017930:Genes, Reporter; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D011839:Radiation, Ionizing; D011995:Recombination, Genetic; D012854:Sister Chromatid Exchange
chemical_list: D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D004247:DNA