Takao Masashi, Kanno Shin-ichiro, Shiromoto Tatsuya, Hasegawa Rei, Ide Hiroshi, Ikeda Shogo, Sarker Altaf H, Seki Shuji, Xing James Z, Le X Chris, Weinfeld Michael, Kobayashi Kumiko, Miyazaki Jun-ichi, Muijtjens Manja, Hoeijmakers Jan H J, van der Horst Gijsbertus, Yasui Akira
Department of Molecular Genetics, Institute of Development, Aging and Cancer, Tohoku University, Sendai 980-8575, Japan.
EMBO J. 2002 Jul 1;21(13):3486-93. doi: 10.1093/emboj/cdf350.
Endonuclease III, encoded by nth in Escherichia coli, removes thymine glycols (Tg), a toxic oxidative DNA lesion. To determine the biological significance of this repair in mammals, we established a mouse model with mutated mNth1, a homolog of nth, by gene targeting. The homozygous mNth1 mutant mice showed no detectable phenotypical abnormality. Embryonic cells with or without wild-type mNth1 showed no difference in sensitivity to menadione or hydrogen peroxide. Tg produced in the mutant mouse liver DNA by X-ray irradiation disappeared with time, though more slowly than in the wild-type mouse. In extracts from mutant mouse liver, we found, instead of mNTH1 activity, at least two novel DNA glycosylase activities against Tg. One activity is significantly higher in the mutant than in wild-type mouse in mitochondria, while the other is another nuclear glycosylase for Tg. These results underscore the importance of base excision repair of Tg both in the nuclei and mitochondria in mammals.
由大肠杆菌中的nth编码的核酸内切酶III可去除胸腺嘧啶乙二醇（Tg），这是一种有毒的氧化性DNA损伤。为了确定这种修复在哺乳动物中的生物学意义，我们通过基因靶向建立了一个具有突变的mNth1（nth的同源物）的小鼠模型。纯合的mNth1突变小鼠未表现出可检测到的表型异常。有或没有野生型mNth1的胚胎细胞对甲萘醌或过氧化氢的敏感性没有差异。通过X射线照射在突变小鼠肝脏DNA中产生的Tg会随时间消失，尽管比野生型小鼠消失得更慢。在突变小鼠肝脏的提取物中，我们发现，除了mNTH1活性外，至少还有两种针对Tg的新型DNA糖基化酶活性。一种活性在突变小鼠线粒体中比野生型小鼠中显著更高，而另一种是针对Tg的另一种核糖基化酶。这些结果强调了哺乳动物细胞核和线粒体中Tg碱基切除修复的重要性。
