Correlation between mechanical strength of messenger RNA pseudoknots and ribosomal frameshifting
Correlation between mechanical strength of messenger RNA pseudoknots and ribosomal frameshifting
复制标题
DOI：
10.1073/pnas.0608668104
复制
发表时间：
2007-04-03
影响因子：
11.1
通讯作者：
Sorensen, Michael A.
中科院分区：
文献类型：
--
作者：
Hansen, Thomas M.;Reihani, S. Nader S.;Sorensen, Michael A.
程序性核糖体移码经常被包括艾滋病毒在内的病毒病原体使用。一些mRNA中存在的光滑序列会导致核糖体移动阅读框架。由此得到的蛋白质由滑序列上游的一个阅读框和滑序列下游的另一个阅读框编码。虽然其机制还不是很清楚，但已知的是，像伪结这样的信使核糖核酸结构会刺激移码。在这里，我们证明了移帧的效率与伪结的机械强度有关。使用了来自传染性支气管炎病毒的两个假结节，第一个茎中有一个碱基对不同。在大肠杆菌中，这两个伪结点导致的移码频率相差两倍。我们用光学镊子来揭开假结。产生最高程度的帧移位的伪结需要比另一个大近2倍的展开力。观测到的能量差异不能用任何现有的模型来解释。我们认为核糖体移码的程度与核糖体假结的机械强度有关。我们的观察结果支持‘’9 Angstrom模型，该模型预测需要一些物理屏障才能迫使核糖体进入-1框架。此外，我们的发现支持最近由冷冻电子显微镜所做的观察，即核糖体和假结之间的机械相互作用导致A位tRNA的变形。这一结果对于理解遗传调控、阅读框架的维持、tRNA的移动以及核糖体对mRNA二级结构的解旋具有重要意义。
Programmed ribosomal frameshifting is often used by viral pathogens including HIV. Slippery sequences present in some mRNAs cause the ribosome to shift reading frame. The resulting protein is thus encoded by one reading frame upstream from the slippery sequence and by another reading frame downstream from the slippery sequence. Although the mechanism is not well understood, frameshifting is known to be stimulated by an mRNA structure such as a pseudoknot. Here, we show that the efficiency of frameshifting relates to the mechanical strength of the pseudoknot. Two pseudoknots derived from the infectious Bronchitis Virus were used, differing by one base pair in the first stem. In Escherichia coli, these two pseudoknots caused frameshifting frequencies that differed by a factor of two. We used optical tweezers to unfold the pseudoknots. The pseudoknot giving rise to the highest degree of frameshifting required a nearly 2-fold larger unfolding force than the other. The observed energy difference cannot be accounted for by any existing model. We propose that the degree of ribosomal frameshifting is related to the mechanical strength of RNA pseudoknots. Our observations support the '' 9 angstrom model" that predicts some physical barrier is needed to force the ribosome into the -1 frame. Also, our findings support the recent observation made by cryoelectron microscopy that mechanical interaction between a ribosome and a pseudoknot causes a deformation of the A-site tRNA. The result has implications for the understanding of genetic regulation, reading frame maintenance, tRNA movement, and unwinding of mRNA secondary structures by ribosomes.