Watanabe Takayoshi, Tashiro Ryu, Sugiyama Hiroshi
Division of Biofunctional Molecules, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, 2-3-10 Surugadai, Kanda, Chiyoda, Tokyo, Japan.
J Am Chem Soc. 2007 Jul 4;129(26):8163-8. doi: 10.1021/ja0692736. Epub 2007 Jun 12.
The photoreactivities of 5-halouracil-containing DNA have widely been used for analysis of protein-DNA interactions and have recently been used for probing charge-transfer processes along DNA. Despite such practical usefulness, the detailed mechanisms of the photochemistry of 5-halouracil-containing DNA are not well understood. We recently discovered that photoirradiation of BrU-substituted DNA efficiently produced 2'-deoxyribonolactone at 5'-(G/C)AABrUBrU-3' and 5'-(G/C)ABrUBrU-3' sequences in duplex DNA. Using synthetic oligonucleotides, we found that similar photoreactivities were maintained at the 5'-(G/C)AABrUT-3' sequence, providing ribonolactone as a major product with concomitant release of adenine base. In this paper, the photoreactivities of various oligonucleotides possessing the 5'-BrUT-3' sequence were examined to elucidate the essential factors of this photoreaction. HPLC product analysis indicated that the yield of 2'-deoxyribonolactone largely depends on the ionization potential of the purine derivatives located 5'-upstream of 5'-BrUT-3', as well as the electron-donating ability of their pairing cytosine derivatives. Oligonucleotides that possess G in the complementary strand provided the ribonolactone with almost the same efficiency. These results clearly suggest that the photoinduced charge transfer from the G-5' upstream of 5'-BrUT-3' sequence, in the same strand and the complementary strand, initiates the reaction. To examine the role of intervening A/T base pair(s) between the G/C and the 5'-BrUT-3' sequence, the photoreactivities of a series of oligonucleotides with different numbers of intervening A/T base pairs were examined. The results revealed that the hotspot sequence consists of the electron-donating G/C base pair, the 5'-BrUT-3' sequence as an acceptor, and an appropriate number of A/T base pairs as a bridge for the charge-transfer process.
含5-卤代尿嘧啶的DNA的光反应活性已被广泛用于分析蛋白质与DNA的相互作用，并且最近被用于探究沿DNA的电荷转移过程。尽管具有如此实际的用途，但含5-卤代尿嘧啶的DNA光化学的详细机制仍未得到很好的理解。我们最近发现，对溴尿嘧啶（BrU）取代的DNA进行光照射可在双链DNA中的5'-(G/C)AABrUBrU-3'和5'-(G/C)ABrUBrU-3'序列中高效产生2'-脱氧核糖内酯。使用合成寡核苷酸，我们发现5'-(G/C)AABrUT-3'序列保持了相似的光反应活性，产生核糖内酯作为主要产物，并伴随腺嘌呤碱基的释放。在本文中，研究了各种具有5'-BrUT-3'序列的寡核苷酸的光反应活性，以阐明该光反应的关键因素。高效液相色谱（HPLC）产物分析表明，2'-脱氧核糖内酯的产率很大程度上取决于位于5'-BrUT-3'上游5'端的嘌呤衍生物的电离势，以及其配对胞嘧啶衍生物的供电子能力。互补链中含有鸟嘌呤（G）的寡核苷酸产生核糖内酯的效率几乎相同。这些结果清楚地表明，来自5'-BrUT-3'序列上游5'端的鸟嘌呤在同一条链和互补链中的光诱导电荷转移引发了该反应。为了研究鸟嘌呤/胞嘧啶（G/C）与5'-BrUT-3'序列之间插入的腺嘌呤/胸腺嘧啶（A/T）碱基对的作用，研究了一系列具有不同数量插入A/T碱基对的寡核苷酸的光反应活性。结果表明，热点序列由供电子的G/C碱基对、作为受体的5'-BrUT-3'序列以及适量的A/T碱基对组成，后者作为电荷转移过程的桥梁。
