Holland J A, Hoffman D W
Department of Chemistry and Biochemistry, University of Texas at Austin 78712, USA.
Nucleic Acids Res. 1996 Jul 15;24(14):2841-8. doi: 10.1093/nar/24.14.2841.
A 30 nt RNA with a sequence designed to form an intramolecular triple helix was analyzed by one-and two-dimensional NMR spectroscopy and UV absorption measurements. NMR data show that the RNA contains seven pyrimidine-purine-pyrimidine base triples stabilized by Watson-Crick and Hoogsteen interactions. The temperature dependence of the imino proton resonances, as well as UV absorption data, indicate that the triple helix is highly stable at acidic pH, melting in a single sharp transition centered at 62 degrees C at pH 4.3. The Watson-Crick and Hoogsteen pairings are disrupted simultaneously upon melting. The NMR data are consistent with a structural model where the Watson-Crick paired strands form an A-helix. Results of model building, guided by NMR data, suggest a possible hydrogen bond between the 2' hydroxyl proton of the Hoogsteen strand and a phosphate oxygen of the purine strand. The structural model is discussed in terms of its ability to account for some of the differences in stability reported for RNA and DNA triple helices and provides insight into features that are likely to be important in the design of RNA binding compounds.
对一段设计为形成分子内三链螺旋结构的30个核苷酸的RNA进行了一维和二维核磁共振光谱分析以及紫外吸收测量。核磁共振数据表明，该RNA含有7个通过沃森-克里克和 hoogsteen相互作用稳定的嘧啶-嘌呤-嘧啶碱基三联体。亚氨基质子共振的温度依赖性以及紫外吸收数据表明，该三链螺旋在酸性pH条件下高度稳定，在pH 4.3时于62℃处发生单一尖锐转变而解链。解链时，沃森-克里克配对和 hoogsteen配对同时被破坏。核磁共振数据与一个结构模型相符，即沃森-克里克配对的链形成一个A-螺旋。在核磁共振数据的指导下进行的模型构建结果表明，hoogsteen链的2'羟基质子与嘌呤链的一个磷酸氧之间可能存在氢键。从该结构模型解释RNA和DNA三链螺旋稳定性差异的能力方面进行了讨论，并为RNA结合化合物设计中可能重要的特征提供了见解。
