Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia), Cantoblanco, 28049 Madrid, Spain.
J Am Chem Soc. 2013 Jan 9;135(1):122-31. doi: 10.1021/ja3054755. Epub 2012 Dec 24.
Double-stranded (ds) RNA is the genetic material of a variety of viruses and has been recently recognized as a relevant molecule in cells for its regulatory role. Despite that the elastic response of dsDNA has been thoroughly characterized in recent years in single-molecule stretching experiments, an equivalent study with dsRNA is still lacking. Here, we have engineered long dsRNA molecules for their individual characterization contrasting information with dsDNA molecules of the same sequence. It is known that dsRNA is an A-form molecule unlike dsDNA, which exhibits B-form in physiological conditions. These structural types are distinguished at the single-molecule level with atomic force microscopy (AFM) and are the basis to understand their different elastic response. Force-extension curves of dsRNA with optical and magnetic tweezers manifest two main regimes of elasticity, an entropic regime whose end is marked by the A-form contour-length and an intrinsic regime that ends in a low-cooperative overstretching transition in which the molecule extends to 1.7 times its A-form contour-length. DsRNA does not switch between the A and B conformations in the presence of force. Finally, dsRNA presents both a lower stretch modulus and overstretching transition force than dsDNA, whereas the electrostatic and intrinsic contributions to the persistence length are larger.
双链 RNA 是多种病毒的遗传物质，最近因其在细胞中的调节作用而被认为是一种相关分子。尽管双链 DNA 的弹性响应在近年来的单分子拉伸实验中得到了彻底的研究，但同样的研究在双链 RNA 中仍然缺乏。在这里，我们设计了长双链 RNA 分子，以便对其进行单独的特征描述，同时与相同序列的双链 DNA 分子进行对比，以获取相关信息。众所周知，双链 RNA 是 A 型分子，而不像 dsDNA 在生理条件下表现出 B 型。这些结构类型在原子力显微镜 (AFM) 水平上得到区分，是理解它们不同弹性响应的基础。使用光学和磁镊的双链 RNA 力-延伸曲线表现出两种主要的弹性状态，一种是熵状态，其末端由 A 型构象长度标记，另一种是内在状态，其末端是一个低协同过度拉伸转变，在该转变中，分子延伸至其 A 型构象长度的 1.7 倍。在力的作用下，双链 RNA 不会在 A 型和 B 型构象之间切换。最后，双链 RNA 的拉伸模量和过度拉伸转变力均低于双链 DNA，而静电和内在对持久性长度的贡献更大。
