Panyutin I G, Neumann R D
Department of Nuclear Medicine, Warren G.Magnuson Clinical Center, National Institutes of Health, Bethesda , MD 20892, USA.
Nucleic Acids Res. 1997 Feb 15;25(4):883-7. doi: 10.1093/nar/25.4.883.
The distribution of breaks produced in both strands of a DNA duplex by the decay of 125I carried by a triplex-forming DNA oligonucleotide was studied at single nucleotide resolution. The 125I atom was located in the C5 position of a single cytosine residue of an oligonucleotide designed to form a triple helix with the target sequence duplex. The majority of the breaks (90%) are located within 10 bp around the decay site. The addition of the free radical scavenger DMSO produces an insignificant effect on the yield and distribution of the breaks. These results suggest that the majority of these breaks are produced by the direct action of radiation and are not mediated by diffusible free radicals. The frequency of breaks in the purine strand was two times higher that in the pyrimidine strand. This asymmetry in the yield of breaks correlates with the geometry of this type of triplex; the C5 of the cytosine in the third strand is closer to the sugar-phosphate backbone of the purine strand. Moreover, study of molecular models shows that the yield of breaks at individual bases correlates with distance from the 125I decay site. We suggest the possible use of 125I decay as a probe for the structure of nucleic acids and nucleoprotein complexes.
在单核苷酸分辨率下，研究了由形成三链的DNA寡核苷酸携带的125I衰变在DNA双链体两条链中产生的断裂分布。125I原子位于设计与靶序列双链体形成三链螺旋的寡核苷酸单个胞嘧啶残基的C5位置。大多数断裂（90%）位于衰变位点周围10个碱基对范围内。添加自由基清除剂二甲基亚砜对断裂的产率和分布产生的影响不显著。这些结果表明，这些断裂中的大多数是由辐射的直接作用产生的，而不是由可扩散的自由基介导的。嘌呤链中的断裂频率比嘧啶链高两倍。这种断裂产率的不对称与这种类型三链的几何结构相关；第三条链中胞嘧啶的C5更靠近嘌呤链的糖磷酸骨架。此外，分子模型研究表明，单个碱基处的断裂产率与距125I衰变位点的距离相关。我们建议将125I衰变用作核酸和核蛋白复合物结构的探针。
