Jackson A L, Loeb L A
Joseph Gottstein Memorial Cancer Research Laboratory, Department of Pathology, University of Washington, Seattle, WA 98195-7705, USA.
Mutat Res. 2000 Feb 14;447(2):187-98. doi: 10.1016/s0027-5107(99)00206-7.
Damage to DNA by reactive oxygen species may be a significant source of endogenous mutagenesis in aerobic organisms. Using a selective assay for microsatellite instability in E. coli, we have asked whether endogenous oxidative mutagenesis can contribute to genetic instability. Instability of repetitive sequences, both in intronic sequences and within coding regions, is a hallmark of genetic instability in human cancers. We demonstrate that exposure of E. coli to low levels of hydrogen peroxide increases the frequency of expansions and deletions within dinucleotide repetitive sequences. Sequencing of the repetitive sequences and flanking non-repetitive regions in mutant clones demonstrated the high specificity for alterations with the repeats. All of the 183 mutants sequenced displayed frameshift alterations within the microsatellite repeats, and no base substitutions or frameshift mutations occurred within the flanking non-repetitive sequences. We hypothesize that endogenous oxidative damage to DNA can increase the frequency of strand slippage intermediates occurring during DNA replication or repair synthesis, and contribute to genomic instability.
活性氧对DNA的损伤可能是需氧生物内源性诱变的一个重要来源。我们利用一种针对大肠杆菌微卫星不稳定性的选择性检测方法，探究内源性氧化诱变是否会导致基因不稳定。内含子序列和编码区域内重复序列的不稳定性是人类癌症中基因不稳定的一个标志。我们证明，将大肠杆菌暴露于低水平的过氧化氢中会增加二核苷酸重复序列内扩增和缺失的频率。对突变克隆中重复序列和侧翼非重复区域进行测序，结果表明突变对重复序列具有高度特异性。测序的183个突变体在微卫星重复序列内均显示移码改变，而侧翼非重复序列内未发生碱基替换或移码突变。我们推测，DNA的内源性氧化损伤会增加DNA复制或修复合成过程中发生链滑动中间体的频率，并导致基因组不稳定。
