Bose S N, Davies R J
Nucleic Acids Res. 1984 Oct 25;12(20):7903-14. doi: 10.1093/nar/12.20.7903.
Photoaddition between adjacent adenine and thymine bases occurs, with a quantum yield of approximately 5 X 10(-4) mol einstein-1, when d(T-A), dT-A, d(pT-A), d(T-A-T), d(T-A-T-A) and poly(dA-dT) are irradiated, at 254 nm, in aqueous solution. The photoadduct thus formed is specifically degraded by acid to the fluorescent heterocyclic base 6-methylimidazo[4,5-b]pyridin-5-one (6-MIP) with retention of C(8) of adenine and the methyl group of thymine. This reaction, coupled with either spectrofluorimetric or radiochemical assay of 6-MIP isolated by high voltage paper electrophoresis, has been used to demonstrate formation of the adenine-thymine photoadduct on UV irradiation of poly(dA-dT).poly(dA-dT) and both native and denatured DNA from calf thymus and E. coli. Estimated quantum yields for this new type of photoreaction in DNA show that it is substantially quenched by base pairing. Possible biological implications of the photoreaction are discussed.
当d(T-A)、dT-A、d(pT-A)、d(T-A-T)、d(T-A-T-A)和聚(dA-dT)在254nm波长下于水溶液中辐照时，相邻的腺嘌呤和胸腺嘧啶碱基之间会发生光加成反应，量子产率约为5×10⁻⁴mol爱因斯坦⁻¹。如此形成的光加合物经酸特异性降解为荧光杂环碱6-甲基咪唑并[4,5-b]吡啶-5-酮（6-MIP），同时保留腺嘌呤的C(8)和胸腺嘧啶的甲基。该反应与通过高压纸电泳分离的6-MIP的荧光光谱法或放射化学分析法相结合，已用于证明在聚(dA-dT)·聚(dA-dT)以及来自小牛胸腺和大肠杆菌的天然和变性DNA经紫外线辐照后腺嘌呤-胸腺嘧啶光加合物的形成。DNA中这种新型光反应的估计量子产率表明，它会因碱基配对而大幅淬灭。文中讨论了该光反应可能的生物学意义。
