Yoon Jung-Hoon, Iwai Shigenori, O'Connor Timothy R, Pfeifer Gerd P
Division of Biology, Beckman Research Institute of the City of Hope, Duarte, CA 91010, USA.
Nucleic Acids Res. 2003 Sep 15;31(18):5399-404. doi: 10.1093/nar/gkg730.
The repair enzymes thymine DNA glycosylase (TDG) and methyl-CpG-binding protein 4 (MBD4) remove thymines from T:G mismatches resulting from deamination of 5-methylcytosine. Thymine glycol, a common DNA lesion produced by oxidative stress, can arise from oxidation of thymine or from oxidative deamination of 5-methylcytosine, and is then present opposite adenine or opposite guanine, respectively. Here we have used oligonucleotides with thymine glycol incorporated into different sequence contexts and paired with adenine or guanine. We show that TDG and MBD4 can remove thymine glycol when present opposite guanine but not when paired with adenine. The efficiency of these enzymes for removal of thymine glycol is about half of that for removal of thymine in the same sequence context. The two proteins may have evolved to act specifically on DNA mismatches produced by deamination and by oxidation-coupled deamination of 5-methylcytosine. This repair pathway contributes to mutation avoidance at methylated CpG dinucleotides.
修复酶胸腺嘧啶DNA糖基化酶（TDG）和甲基CpG结合蛋白4（MBD4）可从5-甲基胞嘧啶脱氨基产生的T:G错配中去除胸腺嘧啶。胸腺嘧啶二醇是氧化应激产生的常见DNA损伤，可由胸腺嘧啶氧化或5-甲基胞嘧啶氧化脱氨基产生，然后分别与腺嘌呤或鸟嘌呤相对存在。在这里，我们使用了掺入胸腺嘧啶二醇的寡核苷酸，这些寡核苷酸处于不同的序列背景中，并与腺嘌呤或鸟嘌呤配对。我们发现，当胸腺嘧啶二醇与鸟嘌呤相对时，TDG和MBD4可以将其去除，但与腺嘌呤配对时则不能。在相同序列背景下，这些酶去除胸腺嘧啶二醇的效率约为去除胸腺嘧啶效率的一半。这两种蛋白质可能已经进化为专门作用于由5-甲基胞嘧啶脱氨基和氧化偶联脱氨基产生的DNA错配。这种修复途径有助于避免甲基化CpG二核苷酸处的突变。
