Yamamura Eiji, Nunoshiba Tatsuo, Nohmi Takehiko, Yamamoto Kazuo
Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan.
Biochem Biophys Res Commun. 2003 Jun 27;306(2):570-6. doi: 10.1016/s0006-291x(03)01027-1.
Damage to DNA by reactive oxygen species may be a significant source of endogenous mutagenesis in aerobic organisms. Using an endogenous tonB gene as a mutation selective marker in Escherichia coli, we have examined whether endogenous oxidative mutagenesis can contribute to genetic instability. We have also used oxyR(+) and oxyR(-) strains to evaluate how hydrogen peroxide scavenging system can contribute to genetic instability. The highest mutation frequency induced by hydrogen peroxide was 3.8x10(-6) at 600 microM and 5.3 x 10(-6) at 40 microM in oxyR(+) and oxyR(-), respectively. Hydrogen peroxide induced minus frameshift mutations predominantly followed by transversions (G:C-->T:A, G:C-->C:G, and A:T-->T:A). The types and the nature of the mutations did not differ between strains. Frameshift mutations occurred at G:C and A:T sites equally, and in repeated and non-repeated sequences equally. It is evident that endogenous oxidative damage to DNA can increase the frequency of strand slippage intermediates occurring during DNA replication and contribute to genomic instability. Our results further indicate that oxyR regulon does not take part in the DNA-repair pathway against oxidative damage induced by hydrogen peroxide.
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。我们利用大肠杆菌中的内源性tonB基因作为突变选择标记，研究了内源性氧化诱变是否会导致遗传不稳定。我们还使用了oxyR(+)和oxyR(-)菌株来评估过氧化氢清除系统如何导致遗传不稳定。在oxyR(+)菌株中，600微摩尔时过氧化氢诱导的最高突变频率为3.8×10(-6)，在oxyR(-)菌株中，40微摩尔时为5.3×10(-6)。过氧化氢主要诱导负移码突变，随后是颠换（G:C→T:A、G:C→C:G和A:T→T:A）。菌株之间的突变类型和性质没有差异。移码突变在G:C和A:T位点以及重复和非重复序列中出现的频率相同。很明显，DNA的内源性氧化损伤会增加DNA复制过程中发生的链滑动中间体的频率，并导致基因组不稳定。我们的结果进一步表明，oxyR调节子不参与对抗过氧化氢诱导的氧化损伤的DNA修复途径。
