Durand J, Birdsell J, Wills C
Department of Biology, University of California, San Diego, La Jolla 92093.
Mutat Res. 1993 Dec;290(2):239-47. doi: 10.1016/0027-5107(93)90164-b.
Sexual (MAT a/alpha) and asexual (MAT a/a) strains of the yeast Saccharomyces cerevisiae, which are completely isogenic except at the MAT locus, were compared in their response to ultraviolet radiation. The effects of UV on survival, mitotic intragenic recombination, photoreactivation, and transformation efficiency with UV-irradiated plasmid DNA were examined. The sexual strain had enhanced survival and higher rates of mitotic intragenic recombination compared with the asexual strain. Exposure to visible light subsequent to irradiation increased the survival of both sexual and asexual strains, and decreased their rates of mitotic intragenic recombination. Similar results were obtained by Haladus and Zuk (1980) in their examination of sexual strains homozygous for rad6-1, and wild-type sexuals. Our sexual strain was also consistently more proficient at transforming plasmid DNA, whether that DNA had been irradiated or not. When pre-irradiated with 25 J/m2 of UV, MAT a/alpha cells transformed more efficiently than MAT a/a cells. When subsequently exposed to light, the ability of these pre-irradiated cells to transform decreased for both strains with increasing irradiation of the plasmid. A smaller decrease in transformation efficiency occurred when cells of both strains were kept in the dark. When pre-irradiated with 100 J/m2, the MAT a/alpha cells showed a 2-fold increase in their transformation efficiency of both irradiated and unirradiated plasmids by up to 2-fold, a phenomenon not seen in the MAT a/a cells even when pre-irradiated with much higher doses of UV. This increase in transformation efficiency was not, however, seen in the MAT a/alpha cells when they were exposed to visible light after UV irradiation. These results suggest that cells with the MAT a/alpha genotype have a UV-inducible system that increases the efficiency of transformation in the absence of visible light. This increase in transformation is not an induced increase in the repair of plasmid DNA, but rather an increase in the ability of pre-irradiated MAT a/alpha cells to take up exogenous DNA. MAT a/a cells do not appear to have a similarly inducible system. To the best of our knowledge, this phenomenon has not been previously reported.
酿酒酵母的有性（MAT a/α）和无性（MAT a/a）菌株，除了MAT位点外完全同基因，对它们对紫外线辐射的反应进行了比较。研究了紫外线对存活、有丝分裂基因内重组、光复活以及用紫外线照射的质粒DNA进行转化效率的影响。与无性菌株相比，有性菌株具有更高的存活率和更高的有丝分裂基因内重组率。照射后暴露于可见光下增加了有性和无性菌株的存活率，并降低了它们的有丝分裂基因内重组率。Haladus和Zuk（1980年）在研究rad6-1纯合的有性菌株和野生型有性菌株时也得到了类似的结果。我们的有性菌株在转化质粒DNA方面也一直更高效，无论该DNA是否经过照射。当用25 J/m2的紫外线预照射时，MAT a/α细胞比MAT a/a细胞转化更有效。当随后暴露于光下时，随着质粒照射量的增加，这两种预照射细胞的转化能力都下降。当两种菌株的细胞都保持在黑暗中时，转化效率的下降较小。当用100 J/m2预照射时，MAT a/α细胞对照射和未照射的质粒的转化效率提高了2倍，即使MAT a/a细胞用更高剂量的紫外线预照射，也没有观察到这种现象。然而，当MAT a/α细胞在紫外线照射后暴露于可见光下时，这种转化效率的提高并未出现。这些结果表明，具有MAT a/α基因型的细胞具有紫外线诱导系统，该系统在没有可见光的情况下会提高转化效率。这种转化的增加不是质粒DNA修复的诱导增加，而是预照射的MAT a/α细胞摄取外源DNA能力的增加。MAT a/a细胞似乎没有类似的诱导系统。据我们所知，这种现象以前尚未报道。
