Tremblay Sébastien, Wagner J Richard
Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
Nucleic Acids Res. 2008 Jan;36(1):284-93. doi: 10.1093/nar/gkm1013. Epub 2007 Nov 21.
Cytosine glycols (5,6-dihydroxy-5,6-dihydrocytosine) are initial products of cytosine oxidation. Because these products are not stable, virtually all biological studies have focused on the stable oxidation products of cytosine, including 5-hydroxycytosine, uracil glycols and 5-hydroxyuracil. Previously, we reported that the lifetime of cytosine glycols was greatly enhanced in double-stranded DNA, thus implicating these products in DNA repair and mutagenesis. In the present work, cytosine and uracil glycols were generated in double-stranded alternating co-polymers by oxidation with KMnO4. The half-life of cytosine glycols in poly(dG-dC) was 6.5 h giving a ratio of dehydration to deamination of 5:1. At high substrate concentrations, the excision of cytosine glycols from poly(dG-dC) by purified endonuclease III was comparable to that of uracil glycols, whereas the excision of these substrates was 5-fold greater than that of 5-hydroxycytosine. Kinetic studies revealed that the V(max) was several fold higher for the excision of cytosine glycols compared to 5-hydroxycytosine. In contrast to cytosine glycols, uracil glycols did not undergo detectable dehydration to 5-hydroxyuracil. Replacing poly(dG-dC) for poly(dI-dC) gave similar results with respect to the lifetime and excision of cytosine glycols. This work demonstrates the formation of cytosine glycols in DNA and their removal by base excision repair.
胞嘧啶二醇（5,6 - 二羟基 - 5,6 - 二氢胞嘧啶）是胞嘧啶氧化的初始产物。由于这些产物不稳定，几乎所有生物学研究都集中在胞嘧啶的稳定氧化产物上，包括5 - 羟基胞嘧啶、尿嘧啶二醇和5 - 羟基尿嘧啶。此前，我们报道过在双链DNA中胞嘧啶二醇的寿命大大延长，因此表明这些产物与DNA修复和诱变有关。在本研究中，通过用高锰酸钾氧化在双链交替共聚物中生成了胞嘧啶二醇和尿嘧啶二醇。聚（dG - dC）中胞嘧啶二醇的半衰期为6.5小时，脱水与脱氨的比例为5:1。在高底物浓度下，纯化的核酸内切酶III从聚（dG - dC）中切除胞嘧啶二醇的效率与切除尿嘧啶二醇的效率相当，而切除这些底物的效率比切除5 - 羟基胞嘧啶的效率高5倍。动力学研究表明，与切除5 - 羟基胞嘧啶相比，切除胞嘧啶二醇的最大反应速度（V(max)）高出几倍。与胞嘧啶二醇不同，尿嘧啶二醇不会发生可检测到的脱水生成5 - 羟基尿嘧啶。用聚（dI - dC）替代聚（dG - dC），在胞嘧啶二醇的寿命和切除方面得到了类似的结果。这项工作证明了DNA中胞嘧啶二醇的形成及其通过碱基切除修复的去除。
