Heilman-Miller S L, Thirumalai D, Woodson S A
Department of Chemistry, University of Mayland, College Park 20742-2021, USA.
J Mol Biol. 2001 Mar 9;306(5):1157-66. doi: 10.1006/jmbi.2001.4437.
Folding of RNA into an ordered, compact structure requires substantial neutralization of the negatively charged backbone by positively charged counterions. Using a native gel electrophoresis assay, we have examined the effects of counterion condensation upon the equilibrium folding of the Tetrahymena ribozyme. Incubation of the ribozyme in the presence of mono-, di- and trivalent ions induces a conformational state that is capable of rapidly forming the native structure upon brief exposure to Mg2+. The cation concentration dependence of this transition is directly correlated with the charge of the counterion used to induce folding. Substrate cleavage assays confirm the rapid onset of catalytic activity under these conditions. These results are discussed in terms of classical counterion condensation theory. A model for folding is proposed which predicts effects of charge, ionic radius and temperature on counterion-induced RNA folding transitions.
RNA折叠成有序、紧密的结构需要带正电荷的抗衡离子大量中和带负电荷的主链。我们使用天然凝胶电泳分析方法，研究了抗衡离子凝聚对嗜热四膜虫核酶平衡折叠的影响。在单价、二价和三价离子存在的情况下孵育核酶，会诱导出一种构象状态，这种构象状态在短暂暴露于Mg2+后能够迅速形成天然结构。这种转变的阳离子浓度依赖性与用于诱导折叠的抗衡离子的电荷直接相关。底物切割分析证实了在这些条件下催化活性的快速启动。这些结果根据经典的抗衡离子凝聚理论进行了讨论。提出了一个折叠模型，该模型预测了电荷、离子半径和温度对抗衡离子诱导的RNA折叠转变的影响。
