Kunz B A, Pierce M K, Mis J R, Giroux C N
Department of Microbiology, University of Manitoba, Winnipeg, Canada.
Mutagenesis. 1987 Nov;2(6):445-53. doi: 10.1093/mutage/2.6.445.
We have characterized mutations induced in the SUP4-o gene of Saccharomyces cerevisiae by u.v. irradiation. Mutants were selected following treatment with 60 J/m2 u.v. light which reduced cell survival to 10% and increased the SUP4-o mutation frequency 100-fold above background. DNA sequence analysis of 120 mutants revealed that u.v. induced all types of base substitutions, although transitions, in particular G:C----A:T events predominated. In addition, a small number of single base pair deletions and double mutations, occurring in tandem or separated by a few base pairs, were recovered. The base pair substitutions were not distributed randomly in the SUP4-o gene and, with one exception, were all located at sites of adjacent pyrimidines, suggesting that they were targeted by u.v. photolesions. A substantial fraction of the mutations were detected at hotspots for u.v. mutagenesis. The majority of changes occurred at the 3' base of dipyrimidine sequences where both cyclobutane dimers and [6-4]-photoproducts could form. Approximately one-third of the induced base substitutions were found at potential pyrimidine dimer sites where [6-4]-photoproducts would be expected to occur rarely. The possible origins of the induced mutations and the role of cyclobutane dimers as premutational u.v. lesions in yeast are considered.
我们已经对经紫外线照射诱导的酿酒酵母SUP4 - o基因中的突变进行了特征分析。在用60 J/m²紫外线照射处理后筛选突变体，该处理使细胞存活率降至10%，并使SUP4 - o突变频率比背景水平提高了100倍。对120个突变体的DNA序列分析表明，紫外线诱导了所有类型的碱基替换，尽管转换，特别是G:C→A:T事件占主导。此外，还发现了少量单碱基对缺失以及串联出现或相隔几个碱基对的双突变。碱基对替换在SUP4 - o基因中并非随机分布，除了一个例外，所有替换都位于相邻嘧啶位点，这表明它们是由紫外线光损伤靶向的。相当一部分突变是在紫外线诱变热点处检测到的。大多数变化发生在二嘧啶序列的3'碱基处，此处可形成环丁烷二聚体和[6 - 4]光产物。大约三分之一的诱导碱基替换出现在潜在的嘧啶二聚体位点，预计在此处[6 - 4]光产物很少出现。本文考虑了诱导突变的可能起源以及环丁烷二聚体作为酵母中诱变前紫外线损伤的作用。
