Competition between the Rad50 complex and the Ku heterodimer reveals a role for Exo1 in processing double-strand breaks but not telomeres.
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.
Tomita
Kazunori
K
Department of Chemistry, Shizuoka University, 836 Oya, Shizuoka 422-8529, Japan.
Matsuura
Akira
A
Caspari
Thomas
T
Carr
Antony M
AM
Akamatsu
Yufuko
Y
Iwasaki
Hiroshi
H
Mizuno
Ken-ichi
K
Ohta
Kunihiro
K
Uritani
Masahiro
M
Ushimaru
Takashi
T
Yoshinaga
Koichi
K
Ueno
Masaru
M
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
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