Division of Chemistry, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
Org Biomol Chem. 2012 Mar 21;10(11):2318-25. doi: 10.1039/c2ob06966k. Epub 2012 Feb 1.
The (6-4) photoproduct is one of the major damaged bases produced by ultraviolet light in DNA. This lesion is known to be alkali-labile, and strand breaks occur at its sites when UV-irradiated DNA is treated with hot alkali. We have analyzed the product obtained by the alkali treatment of a dinucleoside monophosphate containing the (6-4) photoproduct, by HPLC, NMR spectroscopy, and mass spectrometry. We previously found that the N3-C4 bond of the 5' component was hydrolyzed by a mild alkali treatment, and the present study revealed that the following reaction was the hydrolysis of the glycosidic bond at the 3' component. The sugar moiety of this component was lost, even when a 3'-flanking nucleotide was not present. Glycosidic bond hydrolysis was also observed for a dimer and a trimer containing 5-methyl-2-pyrimidinone, which was used as an analog of the 3' component of the (6-4) photoproduct, and its mechanism was elucidated. Finally, the alkali treatment of a tetramer, d(GT(6-4)TC), yielded 2'-deoxycytidine 5'-monophosphate, while 2'-deoxyguanosine 3'-monophosphate was not detected. This result demonstrated the hydrolysis of the glycosidic bond at the 3' component of the (6-4) photoproduct and the subsequent strand break by β-elimination. It was also shown that the glycosidic bond at the 3' component of the Dewar valence isomer was more alkali-labile than that of the (6-4) photoproduct.
（6-4）光产物是 DNA 中紫外线产生的主要受损碱基之一。这种损伤已知是堿不稳定的，当用堿处理紫外线照射的 DNA 时，在其位点会发生链断裂。我们已经通过 HPLC、NMR 光谱和质谱分析了含有（6-4）光产物的二核苷酸单磷酸经堿处理得到的产物。我们之前发现，5' 组分的 N3-C4 键在温和堿处理下发生水解，本研究揭示了 3' 组分的糖苷键发生水解的情况。即使不存在 3' 侧翼核苷酸，该组分的糖部分也会丢失。含有 5-甲基-2-嘧啶酮的二聚体和三聚体也观察到糖苷键水解，5-甲基-2-嘧啶酮被用作（6-4）光产物 3' 组分的类似物，其机制也得到了阐明。最后，四聚体 d(GT(6-4)TC)的堿处理产生了 2'-脱氧胞苷 5'-单磷酸，而未检测到 2'-脱氧鸟苷 3'-单磷酸。这一结果表明（6-4）光产物 3' 组分的糖苷键水解以及随后的β-消除导致链断裂。还表明，Dewar 价态异构体 3' 组分的糖苷键比（6-4）光产物的更堿不稳定。
