Galli Alvaro, Hafer Kurt, Cervelli Tiziana, Schiestl Robert H
Laboratory of Gene and Molecular Therapy, Institute of Clinical Physiology, CNR, 56124 Pisa, Italy.
J Biomed Biotechnol. 2009;2009:312710. doi: 10.1155/2009/312710. Epub 2009 Oct 12.
The DNA polymerase delta (POL3/CDC2) allele pol3-t of Saccharomyces cerevisiae has previously been shown to be sensitive to methylmethanesulfonate (MMS) and has been proposed to be involved in base excision repair. Our results, however, show that the pol3-t mutation is synergistic for MMS sensitivity with MAG1, a known base excision repair gene, but it is epistatic with rad50Delta, suggesting that POL3 may be involved not only in base excision repair but also in a RAD50 dependent function. We further studied the interaction of pol3-t with rad50Delta by examining their effect on spontaneous, MMS-, UV-, and ionizing radiation-induced intrachromosomal recombination. We found that rad50Delta completely abolishes the elevated spontaneous frequency of intrachromosomal recombination in the pol3-t mutant and significantly decreases UV- and MMS-induced recombination in both POL3 and pol3-t strains. Interestingly, rad50Delta had no effect on gamma-ray-induced recombination in both backgrounds between 0 and 50 Gy. Finally, the deletion of RAD50 had no effect on the elevated frequency of homologous integration conferred by the pol3-t mutation. RAD50 is possibly involved in resolution of replication forks that are stalled by mutagen-induced external DNA damage, or internal DNA damage produced by growing the pol3-t mutant at the restrictive temperature.
酿酒酵母的DNA聚合酶δ（POL3/CDC2）等位基因pol3-t先前已被证明对甲磺酸甲酯（MMS）敏感，并被认为参与碱基切除修复。然而，我们的结果表明，pol3-t突变与已知的碱基切除修复基因MAG1在对MMS敏感性方面具有协同作用，但与rad50Δ呈上位性，这表明POL3可能不仅参与碱基切除修复，还参与一种依赖RAD50的功能。我们通过研究pol3-t与rad50Δ对自发的、MMS诱导的、紫外线诱导的和电离辐射诱导的染色体内重组的影响，进一步研究了它们之间的相互作用。我们发现，rad50Δ完全消除了pol3-t突变体中升高的自发染色体内重组频率，并显著降低了POL3和pol3-t菌株中紫外线和MMS诱导的重组。有趣的是，在0至50 Gy之间，rad50Δ对两种背景下的γ射线诱导的重组均无影响。最后，RAD50的缺失对pol3-t突变赋予的同源整合频率升高没有影响。RAD50可能参与解决由诱变剂诱导的外部DNA损伤或在限制温度下培养pol3-t突变体产生的内部DNA损伤所导致的复制叉停滞。
