An unexpectedly high excision capacity for mispaired 5-hydroxymethyluracil in human cell extracts
An unexpectedly high excision capacity for mispaired 5-hydroxymethyluracil in human cell extracts
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DOI：
10.1073/pnas.97.26.14183
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发表时间：
2000-12-19
影响因子：
11.1
通讯作者：
Sowers, LC
中科院分区：
文献类型：
--
作者：
Rusmintratip, V;Sowers, LC
DNA中胸腺嘧啶的氧化可以在5-羟甲基尿嘧啶（HmU）和腺嘌呤之间产生碱基对。而DNA中5-甲基胞嘧啶（5mC）的氧化和脱胺作用可以在HmU和鸟嘌呤之间产生碱基对。通过在特定位点合成含有HmU的寡核苷酸，观察了HeLa细胞和人成纤维细胞提取物中HmU- dna糖基酶的活性。已经测量了去除与鸟嘌呤错配的HmU- dna糖基酶活性。令人惊讶的是，HmU:G的切除活性比相应的HmU:A的活性高60倍，尽管HmU:A碱基对的预期形成速率是HmU:G碱基对的10倍(7)。HmU:G错配将产生于5mC:G碱基对，如果不进行修复，将引起过渡突变。观察到意想不到的高HmU:G糖基酶活性表明，人类细胞可能比预期更频繁地遇到HmU:G错配。5mC向HmU的转化必须被认为是5mC向T过渡突变产生的潜在途径，这种突变经常在人类肿瘤中发现。
The oxidation of thymine in DNA can generate a base pair between 5-hydroxymethyluracil (HmU) and adenine. whereas the oxidation and deamination of 5-methylcytosine (5mC) in DNA can generate a base pair between HmU and guanine. Using synthetic oligonucleotides containing HmU at a defined site, HmU-DNA glycosylase activities in HeLa cell and human fibroblast cell extracts have been observed. An HmU-DNA glycosylase activity that removes HmU mispaired with guanine has been measured. Surprisingly, the HmU:G excision activity is 60 times greater than the corresponding HmU:A activity, even though the expected rate of formation of the HmU:A base pair exceeds that of the HmU:G base pair by a factor of 10(7). The HmU:G mispair would arise from the 5mC:G base pair, and, if unrepaired, would give rise to a transition mutation. The observation of an unexpectedly high HmU:G glycosylase activity suggests that human cells may encounter the HmU:G mispair much more frequently than expected. The conversion of 5mC to HmU must be considered as a potential pathway for the generation of 5mC to T transition mutations, which are often found in human tumors.