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首页> 外文期刊>Journal of Molecular Biology >The Termination Phase in Protein Synthesis is not Obligatorily Followed by the RRF/EF-G-Dependent Recycling Phase
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The Termination Phase in Protein Synthesis is not Obligatorily Followed by the RRF/EF-G-Dependent Recycling Phase

机译：RRF / EF-G依赖的回收阶段不一定紧随蛋白质合成的终止阶段

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摘要

It is general wisdom that termination of bacterial protein synthesis is obligatorily followed by recycling governed by the factors ribosomal recycling factor (RRF), EF-G, and IF3, where the ribosome dissociates into its subunits. In contrast, a recently described 70S-scanning mode of initiation holds that after termination, scanning of 70S can be triggered by fMet-tRNA to the initiation site of a downstream cistron. Here, we analyze the apparent conflict. We constructed a bicistronic mRNA coding for luciferases and showed with a highly resolved in vitro system that the expression of the second cistron did not at all depend on the presence of active RRF. An in vivo analysis cannot be performed in a straightforward way, since RRF is essential for viability and therefore, the RRF gene cannot be knocked out. However, we found an experimental window, where the RRF amount could be reduced to below 2.5%, and in this situation, the expression of the second cistron of a bicistronic luciferase mRNA was only moderately reduced. Both in vitro and in vivo results suggested that RRF-dependent recycling is not an obligatory step after termination, in agreement with the previous findings concerning 70S-scanning initiation. In this view, recycling after termination is a special case of the general RRF function, which happens whenever fMet-tRNA is not available for triggering 70S scanning. (C) 2016 Elsevier Ltd. All rights reserved.
机译：一般认为，细菌蛋白质合成的终止是强制性的，然后由核糖体再循环因子（RRF），EF-G和IF3决定的再循环，在此核糖体解离成其亚基。相反，最近描述的70S扫描起始模式认为，终止后，fMet-tRNA可以触发70S扫描到下游顺反子的起始位点。在这里，我们分析明显的冲突。我们构建了编码荧光素酶的双顺反子mRNA，并在高度解析的体外系统中显示出第二个顺反子的表达根本不取决于活性RRF的存在。体内分析不能以直接的方式进行，因为RRF对生存力至关重要，因此无法敲除RRF基因。但是，我们发现了一个实验窗口，其中RRF量可以降低到2.5％以下，在这种情况下，双顺反子荧光素酶mRNA的第二个顺反子的表达仅适度降低。体外和体内结果均表明，终止后RRF依赖性回收不是必不可少的步骤，这与先前有关70S扫描启动的发现一致。在这种情况下，终止后的回收是常规RRF功能的特例，只要fMet-tRNA无法用于触发70S扫描，就会发生这种情况。 （C）2016 Elsevier Ltd.保留所有权利。

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