Kraxenberger F, Weber K J, Friedl A A, Eckardt-Schupp F, Flentje M, Quicken P, Kellerer A M
Institute of Radiation Biology, GSF-National Research Center for Environment and Health, Neuherberg, Germany.
Radiat Environ Biophys. 1998 Jul;37(2):107-15. doi: 10.1007/s004110050102.
The spatial distribution of DNA double-strand breaks (DSB) was assessed after treatment of mammalian cells (V79) with densely ionizing radiation. Cells were exposed to beams of heavy charged particles (calcium ions: 6.9 MeV/u, 2.1.10(3) keV/microm; uranium ions: 9.0 MeV/u, 1.4.10(4) keV/microm) at the linear accelerator UNILAC of GSI, Darmstadt. DNA was isolated in agarose plugs and subjected to pulsed-field gel electrophoresis under conditions that separated DNA fragments of size 50 kbp to 5 Mbp. The measured fragment distributions were compared to those obtained after gamma-irradiation and were analyzed by means of a convolution and a deconvolution technique. In contrast to the finding for gamma-radiation, the distributions produced by heavy ions do not correspond to the random breakage model. Their marked overdispersion and the observed excess of short fragments reflect spatial clustering of DSB that extends over large regions of the DNA, up to several mega base pairs (Mbp). At fluences of 0.75 and 1.5/microm2, calcium ions produce nearly the same shape of fragment spectrum, merely with a difference in the amount of DNA entering the gel; this suggests that the DNA is fragmented by individual calcium ions. At a fluence of 0.8/microm2 uranium ions produce a profile that is shifted to smaller fragment sizes in comparison to the profile obtained at a fluence of 0.4/microm2; this suggests cumulative action of two separate ions in the formation of fragments. These observations are not consistent with the expectation that the uranium ions, with their much larger LET, should be more likely to produce single particle action than the calcium ions. However, a consideration of the greater lateral extension of the tracks of the faster uranium ions explains the observed differences; it suggests that the DNA is closely coiled so that even DNA locations several Mbp apart are usually not separated by less than 0. 1 or 0.2 microm.
在用高密电离辐射处理哺乳动物细胞（V79）后，评估了DNA双链断裂（DSB）的空间分布。细胞在位于达姆施塔特的GSI亥姆霍兹重离子研究中心的UNILAC直线加速器上，接受重带电粒子束（钙离子：6.9 MeV/u，2.1×10³ keV/μm；铀离子：9.0 MeV/u，1.4×10⁴ keV/μm）的照射。DNA在琼脂糖块中分离，并在能分离50 kbp至5 Mbp大小DNA片段的条件下进行脉冲场凝胶电泳。将测得的片段分布与γ射线照射后得到的分布进行比较，并通过卷积和反卷积技术进行分析。与γ射线照射的结果不同，重离子产生的分布不符合随机断裂模型。它们明显的过度分散以及观察到的短片段过量反映了DSB的空间聚集，这种聚集延伸到DNA的大片区域，可达几个兆碱基对（Mbp）。在通量为0.75和1.5/μm²时，钙离子产生的片段谱形状几乎相同，只是进入凝胶的DNA量有所不同；这表明DNA是由单个钙离子断裂的。在通量为0.8/μm²时，与通量为0.4/μm²时得到的谱相比，铀离子产生的谱向较小片段大小偏移；这表明在片段形成过程中有两个单独离子的累积作用。这些观察结果与预期不符，即具有大得多的传能线密度（LET）的铀离子应该比钙离子更有可能产生单粒子作用。然而，考虑到速度更快的铀离子径迹的更大横向延伸可以解释观察到的差异；这表明DNA紧密盘绕，以至于即使相距几个Mbp的DNA位置通常也不会被小于0.1或0.2μm的距离隔开。
