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  • DNA repair  (4)
  • Mitotic recombination  (2)
  • 1
    ISSN: 1432-0983
    Keywords: Psoralen sensitivity ; Saccharomyces cerevisiae ; DNA repair ; Oxidative stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The complementation and genetical analysis of yeast mutants sensitive to photoactivated 3-carbethoxy-psoralen define three novel recessive mutant alleles pso-5-1, pso6-1, and pso7-1. Their cross-sensitivity to UV254nm, radiomimetic mutagens, and to chemicals enhancing oxidative stress suggest that these mutants are either impaired in metabolic steps protecting from oxidative stress or in mechanisms of the repair of oxygen-dependent DNA lesions. None of the three novel mutant alleles block the induction of reverse mutation by photoactivated mono- and bi-functional psoralens, nitrogen mustards, or UV254nm.
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  • 2
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; pso4-1 mutant Sporulation ; DNA repair ; Meiotic recombination Induced mutagenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have evaluated the effect of the Saccharomyces cerevisiae pso4-1 mutation in sporulation and DNA repair during meiosis. We have found that pso4-1 cells were arrested in an early step of meiosis, before premeiotic DNA synthesis, and hence did not produce spores. These results suggest that the PSO4 gene may act at the start point of the cell cycle, as do some SPO and CDC genes. The pso4-1 mutant cells are specifically sensitive to 8-MOP- and 3-CPs-photoinduced lesions, and are found to be severely affected in meiotic recombination as well as impaired in the mutagenic response, as previously described for mitosis. This means that the PSO4 gene is important for the repair 8-MOP-photoinduced lesions, mainly double-strand breaks, and the processing of these lesions into recombinogenic intermediates.
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  • 3
    ISSN: 1432-0983
    Keywords: DNA repair ; Heat shock ; Hyperthermia ; Mutagenesis ; pso3-1 mutant ; Psoralen ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A putative tolerance, induced by heat shock (HS), to the lethal and mutagenic effects of 8-methoxypsoralen (8-MOP) photoaddition and hyperthermia was analyzed in Saccharomyces cerevisiae using the wild-type strain N123 and the isogenic DNA repair-deficient mutant pso3-1. In wild-type cells, the HS (38°C for 1 h) did not modify either the survival or the mutation frequency observed after 8-MOP photoaddition, even though it conferred protection against the lethal effect of hyperthermia (50°C). In the pso3-1 mutant, HS induced an increase of the survival, and a decrease of the mutation frequency, after 8-MOP photoaddition and it also protected against the lethal effect of hyperthermia. The responses induced by HS were specific for 8-MOP photoaddition, since they were not observed after 254 nm ultraviolet-light damage. These results indicate that the protection conferred by HS depends of the type of lesion, and operates through the induction of different repair processes. In the pso3-1 mutant, HS could channel the repair intermediates to and error-free repair pathway.
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  • 4
    ISSN: 1432-0983
    Keywords: Key words Saccharomyces cerevisiae ; SGS1 ; Helicase ; DNA repair
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The Saccharomyces cerevisiae Sgs1 protein, together with Schizosaccharomyces pombe Rqh1 and the human Bloom and Werner proteins, is a DNA helicase of the Escherichia coli RecQ family. Mutation of SGS1 causes premature aging in yeast cells, including the accumulation of extrachromosomal rDNA circles. We have recently shown that Sgs1p interacts with the DNA repair Rad16p protein and is epistatic to Rad16p for UVC, 4-NQO and H2O2 lesions. Therefore we tested sgs1 strains containing mutations in the helicase and C-terminal domains. We demonstrate here that the helicase activity of the Sgs1 is important for most elements of the sgs1 mutation phenotype, including sensitivity to UVC, 4-NQO, H2O2, MMS and hydroxyurea.
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  • 5
    ISSN: 1617-4623
    Keywords: pso4-1 mutation ; Saccharomyces cerevisiae ; Error-prone recombinational repair ; Mitotic recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The induction of mitotic gene conversion and crossing-over inSaccharomyces cerevisiae diploid cells homozygous for thepso4-1 mutation was examined in comparison to the corresponding wild-type strain. Thepso4-1 mutant strain was found to be completely blocked in mitotic recombination induced by photoaddition of mono- and bifunctional psoralen derivatives as well as by mono- (HN1) and bifunctional (HN2) nitrogen mustards or 254 nm UV radiation in both stationary and exponential phases of growth. Concerning the lethal effect, diploids homozygous for thepso4-1 mutation are more sensitive to all agents tested in any growth phase. However, this effect is more pronounced in the G2 phase of the cell cycle. These results imply that the ploidy effect and the resistance of budding cells are under the control of thePSO4 gene. On the other hand, thepso4-1 mutant is mutationally defective for all agents used. Therefore, thepso4-1 mutant has a generalized block in both recombination and mutation ability. This indicates that thePSO4 gene is involved in an error-prone repair pathway which relies on a recombinational mechanism, strongly suggesting an analogy between thepso4-1 mutation and theRecA orLexA mutation ofEscherichia coli.
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  • 6
    ISSN: 1617-4623
    Keywords: pso4-1 mutation ; Saccharomyces cerevisiae ; Mitotic recombination ; 8-Methoxypsoralen photoreaction ; his4 gene duplication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Spontaneous mitotic recombination was examined in the haploid pso4-1 mutant of Saccharomyces cerevisiae and in the corresponding wild-type strain. Using a genetic system involving a duplication of the his4 gene it was shown that the pso4-1 mutation decreases at least fourfold the spontaneous rate of mitotic recombination. The frequency of spontaneous recombination was reduced tenfold in pso4-1 strains, as previously observed in the rad52-1 mutant. However, whereas the rad52-1 mutation specifically reduces gene conversion, the pso4-1 mutation reduces both gene conversion and reciprocal recombination. Induced mitotic recombination was also studied in pso4-1 mutant and wild-type strains after treatment with 8-methoxypsoralen plus UVA and 254 nm UV irradiation. Consistent with previous results, the pso4-1 mutation was found strongly to affect recombination induction.
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