Hampsey D M, Koski R A, Sherman F
Mol Cell Biol. 1986 Dec;6(12):4425-32. doi: 10.1128/mcb.6.12.4425-4432.1986.
The majority of the mutations induced by ICR-170 in both the CYC1 gene (J. F. Ernst et al. Genetics 111:233-241, 1985) and the HIS4 gene (L. Mathison and M. R. Culbertson, Mol. Cell. Biol. 5:2247-2256, 1985) of the yeast Saccharomyces cerevisiae were recently shown to be single G . C base-pair insertions at monotonous runs of two or more G . C base pairs. However, not all sites were equally mutable; in both the CYC1 and HIS4 genes there is a single highly mutable site where a G . C base pair is preferentially inserted at a [sequence in text]. Here we report the ICR-170 mutagen specificity at the SUP4-o tyrosine tRNA gene of yeast. Genetic fine structure analysis and representative DNA sequence determination of ICR-170-induced mutations revealed that there is also a single highly mutable site in SUP4-o and that the mutation is a G . C base-pair insertion at a monotonous run of G . C base pairs. Analysis of DNA sequences encompassing the regions of highly mutable sites for all three genes indicated that the mutable sites are at the bases of potential hairpin structures; this type of structure could not be found at any of the other, less mutable G . C runs in SUP4, CYC1, and HIS4. Based on these results and recent information regarding novel DNA structural conformations, we present a mechanism for ICR-170-induced mutagenesis. (i) ICR-170 preferentially binds to DNA in the beta conformation; factors that increase the temporal stability of this structure, such as adjacent stem-and-loop formation, increase the frequency of ICR-170 binding; (ii) the observed mutagen specificity reflects formation of a preferred ICR-170 intercalative geometry at [sequence in text] sites; (iii) during replication or repair, ICR-170 remains associated with the single-stranded template; (iv) stuttering or strand slippage by the polymerization complex as it encounters the mutagen results in nucleotide duplication; (v) subsequent replication or mismatch repair fixes the insertion into the genome. This mechanism accounts for both the IRC-170 mutagenic specificity and the molecular basis of the highly mutable sites in S. cerevisiae.
最近研究表明，在酿酒酵母的CYC1基因（J. F. 恩斯特等人，《遗传学》111:233 - 241, 1985）和HIS4基因（L. 马西森和M. R. 卡尔伯森，《分子与细胞生物学》5:2247 - 2256, 1985）中，由ICR - 170诱导产生的大多数突变都是在两个或更多G.C碱基对的单调重复序列处发生单个G.C碱基对的插入。然而，并非所有位点的突变率都相同；在CYC1和HIS4基因中都有一个高度易变的位点，在该位点处G.C碱基对优先插入到[文本中的序列]。在此，我们报告酵母SUP4 - o酪氨酸tRNA基因处的ICR - 170诱变特异性。对ICR - 170诱导的突变进行遗传精细结构分析和代表性DNA序列测定，结果显示SUP4 - o中也有一个高度易变的位点，且该突变是在G.C碱基对的单调重复序列处发生G.C碱基对的插入。对包含这三个基因高度易变位点区域的DNA序列分析表明，这些易变位点位于潜在发夹结构的碱基处；在SUP4、CYC1和HIS4中其他突变率较低的G.C重复序列处均未发现这种结构类型。基于这些结果以及关于新型DNA结构构象的最新信息，我们提出了一种ICR - 170诱导诱变的机制。(i) ICR - 170优先与β构象的DNA结合；增加这种结构时间稳定性的因素，如相邻茎环结构的形成，会增加ICR - 170的结合频率；(ii) 观察到的诱变特异性反映了在[文本中的序列]位点形成了一种优选的ICR - 170嵌入几何结构；(iii) 在复制或修复过程中，ICR - 170仍与单链模板结合；(iv) 聚合复合物在遇到诱变剂时发生口吃或链滑动导致核苷酸重复；(v) 随后的复制或错配修复将插入片段固定到基因组中。该机制解释了IRC - 170的诱变特异性以及酿酒酵母中高度易变位点的分子基础。
