title: Competition between the Rad50 complex and the Ku heterodimer reveals a role for Exo1 in processing double-strand breaks but not telomeres.
abstract: The Mre11-Rad50-Nbs1(Xrs2) complex and the Ku70-Ku80 heterodimer are thought to compete with each other for binding to DNA ends. To investigate the mechanism underlying this competition, we analyzed both DNA damage sensitivity and telomere overhangs in Schizosaccharomyces pombe rad50-d, rad50-d pku70-d, rad50-d exo1-d, and pku70-d rad50-d exo1-d cells. We found that rad50 exo1 double mutants are more methyl methanesulfonate (MMS) sensitive than the respective single mutants. The MMS sensitivity of rad50-d cells was suppressed by concomitant deletion of pku70+. However, the MMS sensitivity of the rad50 exo1 double mutant was not suppressed by the deletion of pku70+. The G-rich overhang at telomere ends in taz1-d cells disappeared upon deletion of rad50+, but the overhang reappeared following concomitant deletion of pku70+. Our data suggest that the Rad50 complex can process DSB ends and telomere ends in the presence of the Ku heterodimer. However, the Ku heterodimer inhibits processing of DSB ends and telomere ends by alternative nucleases in the absence of the Rad50-Rad32 protein complex. While we have identified Exo1 as the alternative nuclease targeting DNA break sites, the identity of the nuclease acting on the telomere ends remains elusive.
authors.affiliation: Department of Chemistry, Shizuoka University, 836 Oya, Shizuoka 422-8529, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Tomita
authors.forename: Akira
authors.initials: A
authors.lastname: Matsuura
authors.forename: Thomas
authors.initials: T
authors.lastname: Caspari
authors.forename: Antony M
authors.initials: AM
authors.lastname: Carr
authors.forename: Yufuko
authors.initials: Y
authors.lastname: Akamatsu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Iwasaki
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Mizuno
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Ohta
authors.forename: Masahiro
authors.initials: M
authors.lastname: Uritani
authors.forename: Takashi
authors.initials: T
authors.lastname: Ushimaru
authors.forename: Koichi
authors.initials: K
authors.lastname: Yoshinaga
authors.forename: Masaru
authors.initials: M
authors.lastname: Ueno
mesh_terms: D034961:Antigens, Nuclear / Q000737:chemistry*; D001667:Binding, Competitive; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D004307:Dose-Response Relationship, Radiation; D005090:Exodeoxyribonucleases / Q000378:metabolism*; D019084:Fluorescent Antibody Technique, Indirect; D005720:Gamma Rays; D017353:Gene Deletion; D000072200:Ku Autoantigen; D008741:Methyl Methanesulfonate; D008957:Models, Genetic; D016296:Mutagenesis; D009154:Mutation; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D012568:Schizosaccharomyces; D016615:Telomere / Q000648:ultrastructure*; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D034961:Antigens, Nuclear; D002843:Chromatin; D004268:DNA-Binding Proteins; C086930:RAD50 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D004247:DNA; D008741:Methyl Methanesulfonate; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen