Gaidamakova Elena K, Neumann Ronald D, Panyutin Igor G
Nuclear Medicine Department, National Institutes of Health, Bethesda, MD 20892-1180, USA.
Nucleic Acids Res. 2002 Nov 15;30(22):4960-5. doi: 10.1093/nar/gkf622.
Decay of (125)I produces a shower of low energy electrons (Auger electrons) that cause strand breaks in DNA in a distance-dependent manner with 90% of the breaks located within 10 bp from the decay site. We studied strand breaks in RNA molecules produced by decay of (125)I incorporated into complementary DNA oligonucleotides forming RNA/DNA duplexes with the target RNA. The frequencies and distribution of the breaks were unaffected by the presence of the free radical scavenger dimethyl sulfoxide (DMSO) or by freezing of the samples. Therefore, as was the case with DNA, most of the breaks in RNA were direct rather than caused by diffusible free radicals produced in water. The distribution of break frequencies at individual bases in RNA molecules is narrower, with a maximum shifted to the 3'-end with respect to the distribution of breaks in DNA molecules of the same sequence. This correlates with the distances from the radioiodine to the sugars of the corresponding bases in A-form (RNA/DNA duplex) and B-form (DNA/DNA duplex) DNA. Interestingly, when (125)I was located close to the end of the antisense DNA oligonucleotide, we observed breaks in RNA beyond the RNA/DNA duplex region. This was not the case for a control DNA/DNA hybrid of the same sequence. We assume that for the RNA there is an interaction between the RNA/DNA duplex region and the single-stranded RNA tail, and we propose a model for such an interaction. This report demonstrates that (125)I radioprobing of RNA could be a powerful method to study both local conformation and global folding of RNA molecules.
碘-125（(^{125}I)）衰变会产生一系列低能电子（俄歇电子），这些电子会以距离依赖的方式导致DNA链断裂，其中90%的断裂位于距衰变位点10个碱基对（bp）以内。我们研究了掺入互补DNA寡核苷酸中的碘-125（(^{125}I)）衰变所产生的RNA分子中的链断裂情况，这些互补DNA寡核苷酸与靶RNA形成RNA/DNA双链体。断裂的频率和分布不受自由基清除剂二甲基亚砜（DMSO）的存在或样品冷冻的影响。因此，与DNA的情况一样，RNA中的大多数断裂是直接产生的，而非由水中产生的可扩散自由基导致。RNA分子中各个碱基处的断裂频率分布更窄，相对于相同序列的DNA分子中的断裂分布，最大值向3'端偏移。这与A-型（RNA/DNA双链体）和B-型（DNA/DNA双链体）DNA中放射性碘与相应碱基糖基之间的距离相关。有趣的是，当碘-125（(^{125}I)）靠近反义DNA寡核苷酸的末端时，我们在RNA/DNA双链体区域之外的RNA中观察到了断裂。对于相同序列的对照DNA/DNA杂交体则并非如此。我们假设对于RNA而言，RNA/DNA双链体区域与单链RNA尾部之间存在相互作用，并提出了一个关于这种相互作用的模型。本报告表明，碘-125（(^{125}I)）对RNA的放射性探测可能是研究RNA分子局部构象和整体折叠的有力方法。
