Barone F, Bonincontro A, Mazzei F, Minoprio A, Pedone F
Laboratorio di Fisica, Instituto Superiore di Sanità, Roma, Italy.
Photochem Photobiol. 1995 Jan;61(1):61-7. doi: 10.1111/j.1751-1097.1995.tb09243.x.
It is well known that the pyrimidine dimers are the main damage produced by UV radiation on the DNA structure. However, while studies on the photoproduct structure have been carried out extensively, uncertainties still exist on the implication that a single damaging event has on the overall conformation. In particular, the extension of the damage influence on the polynucleotide chain is a matter of debate. This problem is especially important to understanding some steps of the repair mechanisms. In this study we performed a chemical-physical characterization of 21 base pair oligonucleotides containing a single thymine dimer in one strand. Thermodynamic parameters were determined by means of thermal denaturation experiments, and static fluorescence measurements were performed to unequivocally define the primary structure-conformation relationship in this specific case. We used hydroxyl radicals, produced by means of gamma-irradiation of the sample solution, to detect fine structure changes. Our data show that the introduction of a single thymine dimer might cause only a slight distortion of the helix geometry, as judged by the evaluation of the enthalpic and the entropic terms and by the small changes observed in the binding of ethidium bromide to DNA. The modifications in the sugar phosphate backbone subsequent to the damaging event are especially evident, near the thymine dimer, toward the 5'-end direction in the strand containing the dimer.
众所周知，嘧啶二聚体是紫外线辐射对DNA结构造成的主要损伤。然而，尽管对光产物结构的研究已经广泛开展，但单个损伤事件对整体构象的影响仍存在不确定性。特别是，损伤对多核苷酸链的影响范围是一个有争议的问题。这个问题对于理解修复机制的某些步骤尤为重要。在本研究中，我们对一条链中含有单个胸腺嘧啶二聚体的21碱基对寡核苷酸进行了化学物理表征。通过热变性实验确定了热力学参数，并进行了静态荧光测量，以明确界定这种特定情况下的一级结构-构象关系。我们利用样品溶液的γ辐射产生的羟基自由基来检测精细结构变化。我们的数据表明，通过对焓项和熵项的评估以及溴化乙锭与DNA结合的微小变化判断，单个胸腺嘧啶二聚体的引入可能仅导致螺旋几何结构的轻微扭曲。损伤事件后糖磷酸骨架的修饰在胸腺嘧啶二聚体附近，朝着含有二聚体的链的5'-端方向尤为明显。
