de Serres F J
Center for Life Sciences and Toxicology, Chemistry and Life Sciences, Research Triangle Institute, NC 27709-2194.
Mutat Res. 1994 May 1;307(1):175-84. doi: 10.1016/0027-5107(94)90290-9.
Previous studies on X-ray-induced adenine-3 mutations induced in heterokaryon 12 of Neurospora crassa showed that they consisted of gene/point mutations, multilocus deletion mutations, and 3 different genotypic classes of multiple-locus mutations (designated [-3]IR + RLCL, ad-3R + RLCL, and ad-3R + RL). In the present paper, multiple-locus mutations consisting of gene/point mutations at the ad-3A or the ad-3B locus with sites of recessive lethal damage closely linked to the ad-3 region (designated ad-3R + RLCL) or with sites of recessive lethal damage elsewhere in the genome (designated ad-3R + RL) were analyzed to determine whether they resulted from mutations at the same sites or different sites throughout the genome. It was assumed that if the recessive lethal mutations in individual multiple-locus mutations showed complementation on adenine-supplemented medium, they resulted from mutations at different sites. Multiple-locus mutations from both major genotypic classes were combined, as forced heterokaryons, in all possible pairwise combinations and then were plated out on adenine-supplemented medium. These studies indicated that 89.3% (50/56) of the recessive lethal mutations in these 2 classes of multiple-locus mutations complement one another. Thus, they are presumed to have resulted predominantly from genetic damage at different sites throughout the genome. Within the group of 20 multiple-locus mutations that did not complement in various pairwise combinations, 90% (18/20) appear to map in a region, distal to the ad-3 region, defined by a series of overlapping multilocus deletion mutations in 6 mutations of genotype ad-3R + RLCL. The other 10% (2/20) are located elsewhere on Linkage Group I or elsewhere in the genome. The present data base on multiple-locus mutations is unique; such events either can not be detected, or can only be detected with difficulty, in other eukaryotic specific-locus assay systems such as mammalian cells in culture, Drosophila or mice. Our data on X-ray-induced ad-3 specific-locus mutations from the present and previous studies demonstrate the presence of additional sites of genetic damage, both closely linked with the ad-3 region or elsewhere in the genome, in ad-3 specific-locus mutations. Because the frequencies of each class of multiple-locus mutations is dose-dependent, they must be taken into account in genetic risk assessment exercises. Failure to acknowledge the presence of such additional sites of genetic damage in the utilization of specific-locus data could result in underestimation of the risk of human exposure to environmental mutagens.
先前对粗糙脉孢菌异核体12中X射线诱导的腺嘌呤-3突变的研究表明，它们包括基因/点突变、多位点缺失突变以及3种不同基因型类别的多位点突变（分别命名为[-3]IR + RLCL、ad-3R + RLCL和ad-3R + RL）。在本文中，分析了由ad-3A或ad-3B位点的基因/点突变组成的多位点突变，这些突变的隐性致死损伤位点与ad-3区域紧密连锁（命名为ad-3R + RLCL）或与基因组其他位置的隐性致死损伤位点（命名为ad-3R + RL），以确定它们是由全基因组中相同位点还是不同位点的突变导致的。假设如果单个多位点突变中的隐性致死突变在添加腺嘌呤的培养基上表现出互补作用，那么它们是由不同位点的突变导致的。将来自这两个主要基因型类别的多位点突变作为强制异核体以所有可能的两两组合方式进行合并，然后接种在添加腺嘌呤的培养基上。这些研究表明，这两类多位点突变中89.3%（50/56）的隐性致死突变相互互补。因此，推测它们主要是由全基因组中不同位点的遗传损伤导致的。在20个在各种两两组合中不互补的多位点突变组中，90%（18/20）似乎定位在ad-3区域远端的一个区域，该区域由基因型为ad-3R + RLCL的6个突变中的一系列重叠多位点缺失突变所定义。另外10%（2/20）位于连锁群I的其他位置或基因组的其他地方。目前关于多位点突变的数据库是独一无二的；在其他真核生物特定位点检测系统中，如培养的哺乳动物细胞、果蝇或小鼠中，此类事件要么无法检测到，要么只能很难检测到。我们目前和先前研究中关于X射线诱导的ad-3特定位点突变的数据表明，在ad-3特定位点突变中存在额外的遗传损伤位点，这些位点要么与ad-3区域紧密连锁，要么位于基因组的其他地方。由于每类多位点突变的频率是剂量依赖性的，因此在遗传风险评估中必须考虑到它们。在利用特定位点数据时未能认识到此类额外遗传损伤位点的存在可能会导致低估人类接触环境诱变剂的风险。
