中文摘要：

5-Hydroxymethylcytosine (5hmC )T 甚至是在场的在里面噬菌体和哺乳动物的 DNA。在噬菌体的 5hmC 被 deoxycytidylate hydroxymethylase (CH ) 被 cytosine 底的 hydroxymethylation 在 deoxycytidylate (dCMP ) 形成，它把溶剂水用作氢氧根组施主。由对比， 5hmC 被 5-methylcytosine (5mC ) 的氧化在哺乳动物接合子形成。5hmC 也是在 nucleoside 抗菌素 mildiomycin 的现在，它的形成被 cytidylate hydroxymethylase MilA 管理。然而，催化机制仍然保持未知。在现在的学习，我们净化了他的标注 MilA 并且喂它的在里面有 H2 18O 的 vitro 反应。产品的最小公倍数分析表明 18O 被合并到 hydroxymethylated CMP (HmCMP ) ，和 18O 标签 HmCMP 的第二等的 MS 结果显示 18O 被合并到 HmCMP 的 cytosine。结果证明 MilA 把溶剂水用作象 CH 一样的氢氧根组施主。而且， MilA 的 Thr102 作为潜在的批评氨基酸抛锚被预言为 hydroxylation 的水的一个分子。最后，在微生物引起的染色体的组织上的上下文比较表明原来作为通常认为的 thymidylate synthase (TS ) 注解的六相应 ORF 是更可能的是 CMP hydroxymethylase。

英文摘要：

5-Hydroxymethylcytosine （5hmC） was present in T-even phage and mammalian DNA. 5hmC in phage is formed by hydroxymethylation of the cytosine base in deoxycytidylate （dCMP） by deoxycytidylate hydroxymethylase （CH）, which uses the solvent water as the hydroxyl group donor. By contrast, 5hmC is formed in mammal zygotes by the oxidation of 5-methylcytosine （5mC）. 5hmC was also present in a nucleoside antibiotic mildiomycin and its formation is governed by a cytidylate hydroxymethylase MilA. However, the catalytic mechanism remains unknown. In the present study, we purified His-tagged MilA and fed its in vitro reaction with H2^18O. The LC-MS analysis of the product revealed that ^18O was incorporated into the hydroxymethylated CMP （HmCMP）, and the secondary MS result of ^18O-labeled HmCMP indicated that ^18O was incorporated into the cytosine of HmCMP. The results demonstrate that MilA uses solvent water as the hydroxyl group donor like CH. Moreover, Thr102 of MilA was predicted as potential critical amino acid anchoring one molecule of water for hydroxylation. Finally, organizational context comparison in microbial genomes reveals that six homologous ORFs originally annotated as putative thymidylate synthase （TS） are more likely to be CMP hydroxymethylase.