Evidence for the translation initiation of leaderless mRNAs by the intact 70 S ribosome without its dissociation into subunits in eubacteria
Evidence for the translation initiation of leaderless mRNAs by the intact 70 S ribosome without its dissociation into subunits in eubacteria
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DOI：
10.1074/jbc.m308784200
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发表时间：
2004-03-05
影响因子：
4.8
通讯作者：
Ueda, T
中科院分区：
文献类型：
--
作者：
Udagawa, T;Shimizu, Y;Ueda, T
在真细菌中，70 S核糖体解离成30 S和50 S亚基是具有5'-前导序列的典型mrna翻译起始的必要第一步。然而，在一些真细菌中已经发现了一些以起始密码子开始的无前导mrna。这些已被证明可以在体内有效地翻译。在这里，我们研究了利用大肠杆菌高度重组的无细胞翻译系统启动无领导mRNA翻译的过程。我们发现无前导mRNA优先结合70 S核糖体，无前导mRNA。70年代。即使没有起始因子（if）， fMet-tRNA复合物也可以从起始阶段过渡到延伸阶段。此外，与30 S亚基相比，如果完整的70 S核糖体参与其中，则无前导mRNA翻译的效率更高。此外，过量的IF3抑制无前导mRNA翻译，可能是因为它促进70 S核糖体分解成亚基。最后，过量的fMet-tRNA促进了不依赖if的无前导mRNA的翻译。这些观察结果强烈表明，无前导mRNA翻译是由组装的70s核糖体启动的，因此绕过了解离过程。
In eubacteria, the dissociation of the 70 S ribosome into the 30 S and 50 S subunits is the essential first step for the translation initiation of canonical mRNAs that possess 5'-leader sequences. However, a number of leaderless mRNAs that start with the initiation codon have been identified in some eubacteria. These have been shown to be translated efficiently in vivo. Here we investigated the process by which leaderless mRNA translation is initiated by using a highly reconstituted cell-free translation system from Escherichia coli. We found that leaderless mRNAs bind preferentially to 70 S ribosomes and that the leaderless mRNA . 70 S . fMet-tRNA complex can transit from the initiation to the elongation phase even in the absence of initiation factors ( IFs). Moreover, leaderless mRNA translation proceeds more efficiently if the intact 70 S ribosome is involved compared with the 30 S subunit. Furthermore, excess amounts of IF3 inhibit leaderless mRNA translation, probably because it promotes the disassembly of the 70 S ribosome into subunits. Finally, excess amounts of fMet-tRNA facilitate the IF-independent translation of leaderless mRNA. These observations strongly suggest that leaderless mRNA translation is initiated by the assembled 70 S ribosome and thereby bypasses the dissociation process.