Study of production mechanism of DNA clustered damage in aqueous solution

本研究的目的是验证我们的假设，即DNA的双链断裂（DSB）作为一种簇状损伤，主要产生于一个瞬时存在的区域（热区），在这个区域内，局部区域的许多能量沉积事件高密度地产生自由基。通过改变单色光子的能量，我们可以控制“热区”的大小。由水中产生的二次光电子产生。我们已经观察到单链断裂的效率随着光子能量的降低而提高，而单链断裂则表现出相反的依赖性。在研究期间，我们观察到在高浓度自由基清除剂存在的情况下，链面包诱导的x射线光子能量依赖与不含清除剂的情况相同。这似乎表明我们的假设在细胞内环境中是有效的。为了检验活细胞中双链断裂的产生效率，我们建立了一种不经限制性消化酶处理的细胞DNA双链断裂数测定方法，即脉冲场凝胶电泳。我们很快就会得到我们假设检验的结果。我们还研究了单色真空紫外光子（150 - 180 nm）在水溶液中产生的DNA链断裂。我们发现VUV光子对DSB和SSB产生的能量依赖是不同的，表明这两种类型的断链产生机制是不同的。

Purpose of the study is to test our hypothesis that double strand breaks (DSB) of DNA, as a type of clustered damage, are mainly produced in a transiently-existing area (hot area) in which radicals are produced with high density by many energy deposition events in localized region. By changing the energy of monochromatic photons irradiated to aqueous samples, we can control the dimension of "hot area! Produced by the secondary photoelectron produced in water. We already observed that efficiency of DSB production become larger with lower energy photon, while single strand break (SSB) exhibit opposite dependence.During the term of the study, we have observed that the X-ray photon energy dependence of strand bread induction in the presence of high concentration of radical scavenger is the same with the case of the solution without scavenger. This seems to suggest that our hypothesis is effective in intracellular environment. In order to examine the production efficiency of double strand breaks in living cells, we have established a method to determine the number of double strand break in the cellular DNA without any treatment with restrictive digestion enzyme, by utilizing pulse field gel electrophoresis. We will soon have the answer of the test of our hypothesis.We have also investigated the production of DNA strand breaks by monochromatic vacuum UV photons (150 - 180 nm) in aqueous solution. We have found that VUV photon energy dependence of the production of DSB and SSB is different, indicating that production mechanism for the production of both type of strand breakage is different.