Takamoto Keiji, He Qin, Morris Stephanie, Chance Mark R, Brenowitz Michael
Department of Physiology and Biophysics, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Nat Struct Biol. 2002 Dec;9(12):928-33. doi: 10.1038/nsb871.
The formation of individual tertiary contacts of the Tetrahymena L-21 Sca I ribozyme has been monitored by hydroxyl radical footprinting and its global conformation by analytical ultracentrifugation as a function of monovalent ion concentration in the absence of divalent ions. Advanced methods of data analysis, which allow the hydroxyl radical reactivity of every nucleotide to be quantified, permit monitoring of each and every structural element of the RNA. Monovalent ion-mediated global compaction of the ribozyme is accompanied by the formation of native tertiary contacts; most native tertiary contacts are evident except several that are located near where divalent ions are observed in crystallographic structures. Non-native tertiary contacts are also observed at low but not high concentrations of monovalent ions. In light of recent studies that have shown that the presence of monovalent ions greatly accelerates the Mg2+-dependent folding of the Tetrahymena ribozyme, the present studies suggest that Na+ concentration changes not only the starting position of the RNA on its folding funnel but also pushes it deep into the well by forming native tertiary contacts and, thus, favoring fast and correct folding pathways.
在没有二价离子的情况下，通过羟自由基足迹法监测了嗜热四膜虫L-21 Sca I核酶单个三级接触的形成，并通过分析超速离心法监测了其整体构象随单价离子浓度的变化。先进的数据分析方法能够对每个核苷酸的羟自由基反应性进行量化，从而可以监测RNA的每一个结构元件。核酶的单价离子介导的整体压缩伴随着天然三级接触的形成；除了在晶体结构中观察到二价离子的位置附近的几个接触外，大多数天然三级接触都很明显。在低浓度而非高浓度的单价离子下也观察到了非天然三级接触。鉴于最近的研究表明单价离子的存在极大地加速了嗜热四膜虫核酶的Mg2+依赖性折叠，本研究表明，Na+浓度不仅改变了RNA在其折叠漏斗上的起始位置，还通过形成天然三级接触将其深入推至阱中，从而有利于快速和正确的折叠途径。
