IONIZING RADIATION INDUCED DNA DAMAGE AND REPAIR

这个项目的目标是解释电离辐射是如何导致 癌症，突变和细胞死亡，通过阐明化学和酶学 X射线诱导的DNA损伤和修复。 的新办法 X射线诱导单链断裂和碱基修饰研究 介绍了 我们将使用人类DNA中的重复序列（α序列）来1） 确定伽马辐照后链断裂的位置（顺序） 体外和体内; 2）测定氧合，pH， 温度和自由基清除剂的位置和程度， 链断裂; 3）确定碱不稳定位点的位置（序列） 在伽马辐照的DNA中; 4）确定新的 描述了X射线损伤，3'磷酸乙醇酸末端，在DNA照射， 体外和完整细胞中。 研究X射线诱导的碱基修饰的方法使用灵敏的 “修饰后标记”法。 该方法将用于确定 1)特定碱基修饰的形成水平 γ辐射和2）修复的速度和程度，这种 伽马辐照后的碱基修饰。 选择研究人类修复酶的方法使用DNA底物， 含有由以下物质诱导的单一、确定和放射性标记病变类型 X光片 我们将1）确定人类酶的存在， 含有胸腺嘧啶二醇、HMU和3'磷酸乙醇酸末端的DNA; 2） 利用这些底物分离和表征这些酶; 3)确定这种酶的缺乏是否可以解释 共济失调毛细血管扩张症细胞对X线和拟放射线敏感性 毒品 X射线DNA损伤和修复过程的知识将有助于 制定更合理的癌症预防和治疗方法， 预测低水平辐射的影响。

The goal of this project is to explain how ionizing radiation causes cancer, mutation and cell death by elucidating the chemistry and enzymology of X-ray-induced DNA damage and repair in human cells. New approaches to the study of X-ray-induced single-strand breaks and base-modifications are described. We will use a repeated sequence (alpha sequence) in human DNA to 1) determine the location (sequence) of strand breaks after gamma-irradiation in vitro and in vivo; 2) determine the effect of oxygenation, pH, temperature, and free radical scavengers on the location and extent of strand breaks; 3) determine the location (sequence) of alkali-labile sites in gamma-irradiated DNA; 4) determine the level of production of a newly described X-ray lesion, 3' phosphoglycolate termini, in DNA irradiated in vitro and in intact cells. The approach to study of X-ray induced base modifications uses a sensitive "post-modification labeling" method. This method will be used to determine 1) levels of formation of particular base-modifications after gamma-irradiation and 2) the rates and extent of repair of such base-modifications after gamma irradiation. The approach chosen to study human repair enzymes uses DNA substrates which contain single, defined and radiolabeled lesions of the types induced by X-rays. We will 1) determine the presence of human enzymes specific for DNA containing thymine glycols, HMU and 3' phosphoglycolate termini; 2) utilize such substrates for isolation and characterization of such enzymes; 3) determine whether a deficiency of such an enzyme can explain the susceptibility of ataxia telangiectasia cells to X-rays and radiomimetic drugs. Knowledge of the processes of X-ray DNA damage and repair will be useful in developing more rational approaches to cancer prevention and therapy and in predicting the effects of low level radiation exposure.