DNA damage-inducible and RAD52-independent repair of DNA double-strand breaks in Saccharomyces cerevisiae.
Chromosomal repair was studied in stationary-phase Saccharomyces cerevisiae, including rad52/rad52 mutant strains deficient in repairing double-strand breaks (DSBs) by homologous recombination. Mutant strains suffered more chromosomal fragmentation than RAD52/RAD52 strains after treatments with cobalt-60 gamma irradiation or radiomimetic bleomycin, except after high bleomycin doses when chromosomes from rad52/rad52 strains contained fewer DSBs than chromosomes from RAD52/RAD52 strains. DNAs from both genotypes exhibited quick rejoining following gamma irradiation and sedimentation in isokinetic alkaline sucrose gradients, but only chromosomes from RAD52/RAD52 strains exhibited slower rejoining (10 min to 4 hr in growth medium). Chromosomal DSBs introduced by gamma irradiation and bleomycin were analyzed after pulsed-field gel electrophoresis. After equitoxic damage by both DNA-damaging agents, chromosomes in rad52/rad52 cells were reconstructed under nongrowth conditions [liquid holding (LH)]. Up to 100% of DSBs were eliminated and survival increased in RAD52/RAD52 and rad52/rad52 strains. After low doses, chromosomes were sometimes degraded and reconstructed during LH. Chromosomal reconstruction in rad52/rad52 strains was dose dependent after gamma irradiation, but greater after high, rather than low, bleomycin doses with or without LH. These results suggest that a threshold of DSBs is the requisite signal for DNA-damage-inducible repair, and that nonhomologous end-joining repair or another repair function is a dominant mechanism in S. cerevisiae when homologous recombination is impaired.
Moore
C W
CW
Department of Microbiology and Immunology, City University of New York Medical School/Sophie Davis School of Biomedical Education and Graduate Programs in Biochemistry and Biology, New York, New York 10031, USA. moore@med.cuny.edu
McKoy
J
J
Dardalhon
M
M
Davermann
D
D
Martinez
M
M
Averbeck
D
D
D001761:Bleomycin / Q000494:pharmacology; D015825:Chromosomes, Fungal; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D053938:DNA Fragmentation; D004260:DNA Repair; D004271:DNA, Fungal / Q000187:drug effects / Q000528:radiation effects; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D016521:Electrophoresis, Gel, Pulsed-Field; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology*; D051721:Rad52 DNA Repair and Recombination Protein; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins; D013997:Time Factors
D004271:DNA, Fungal; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C497197:RAD52 protein, S cerevisiae; D051721:Rad52 DNA Repair and Recombination Protein; D029701:Saccharomyces cerevisiae Proteins; D001761:Bleomycin