Unusual knot-like structures recently discovered in viral exoribonuclease-resistant RNAs (xrRNAs) prevent digestion by host RNases to create subgenomic RNAs enhancing infection and pathogenicity. xrRNAs are proposed to prevent digestion through mechanical resistance to unfolding. However, their unfolding force has not been measured, and the factors determining RNase resistance are unclear. Furthermore, how these knots fold remains unknown. Unfolding a Zika virus xrRNA with optical tweezers revealed that it was the most mechanically stable RNA yet observed. The knot formed by threading the 5′ end into a three-helix junction before pseudoknot interactions closed a ring around it. The pseudoknot and tertiary contacts stabilizing the threaded 5′ end were both required to generate extreme force resistance, whereas removing a 5′-end contact produced a low-force knot lacking RNase resistance. These results indicate mechanical resistance plays a central functional role, with the fraction of molecules forming extremely high-force knots determining the RNase resistance level.

最近在病毒外切核糖核酸酶抗性 RNA (xrRNA) 中发现的不寻常的结状结构可阻止宿主 RNase 的消化，从而产生增强感染和致病性的亚基因组 RNA。xrRNA 被提议通过对展开的机械阻力来防止消化。然而，它们的展开力尚未测量，决定 RNase 抗性的因素尚不清楚。此外，这些结如何折叠仍然未知。用光镊展开寨卡病毒 xrRNA 表明它是迄今为止观察到的机械稳定性最高的 RNA。通过在假结相互作用之前将 5' 端拧入三螺旋接头形成的结在其周围闭合一个环。稳定螺纹 5' 端的假结和三次接触都需要产生极强的抗力，而去除 5' 端接触会产生缺乏 RNase 抗性的低力结。这些结果表明机械阻力起着核心的功能作用，形成极高力结的分子部分决定了 RNase 阻力水平。