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首页> 外文期刊>Journal of Molecular Biology >Simultaneous and functional binding of SmpB and EF-Tu center dot GTP to the alanyl acceptor arm of tmRNA
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Simultaneous and functional binding of SmpB and EF-Tu center dot GTP to the alanyl acceptor arm of tmRNA

机译：SmpB和EF-Tu中心点GTP同时结合到功能上的tmRNA的丙氨酸受体臂

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摘要

Transfer-messenger RNA (tmRNA) mimics functions of aminoacyl-tRNA and mRNA, subsequently, when rescuing stalled ribosomes on a 3' truncated mRNA without stop codon in bacteria. In addition, this mechanism marks prematurely terminated proteins by a C-terminal peptide tag as a signal for degradation by specific cellular proteases. For Escherichia coli, previous studies on initial steps of this "trans-translation" mechanism revealed that tmRNA alanylation by Ala-tRNA synthetase and binding of Ala-tmRNA by EF-Tu-GTP for subsequent delivery to stalled ribosomes are inefficient when compared to analogous reactions with canonical tRNA(Ala). In other studies, protein SmpB and ribosomal protein S1 appeared to bind directly to tmRNA and to be indispensable for trans-translation. Here, we have searched for additional and synergistic effects of the latter two on tmRNA alanylation and its subsequent binding to EF-Tu(.)GTP. Kinetic analysis of functioning combined with band-shift experiments and structural probing demonstrate, that tmRNA may indeed form a multimeric complex with SmpB, S1 and EF-Tu(.)GTP, which leads to a considerably enhanced efficiency of the initial steps of trans-translation. Whereas S1 binds to the mRNA region of tmRNA, we have found that SmpB and EF-Tu both interact with its acceptor arm region. Interaction with SmpB and EF-Tu was also observed at the acceptor arm of Ala-tRNA(Ala), but there the alanylation efficiency was inhibited rather than stimulated by SmpB. Therefore, SmpB may function as an essential modulator of the tRNA-like acceptor arm of tmRNA during its successive steps in trans-translation.
机译：随后，当在3'截短的mRNA上解救停滞的核糖体而没有细菌中的终止密码子时，传递信使RNA（tmRNA）模仿氨酰基tRNA和mRNA的功能。此外，该机制通过C端肽标签标记过早终止的蛋白质，作为特定细胞蛋白酶降解的信号。对于大肠杆菌，先前对这种“反式翻译”机制初始步骤的研究表明，与类似物相比，通过Ala-tRNA合成酶进行的tmRNA酰化和通过EF-Tu-GTP进行Ala-tmRNA的结合以随后递送至失速的核糖体效率低下。与典型的tRNA（Ala）反应。在其他研究中，蛋白SmpB和核糖体蛋白S1似乎直接与tmRNA结合，并且对于转译而言必不可少。在这里，我们已经搜索了后两者对tmRNA酰化及其与EF-Tu（。）GTP的后续结合的其他协同作用。对功能的动力学分析，结合带移实验和结构探测表明，tmRNA的确可以与SmpB，S1和EF-Tu（。）GTP形成多聚体复合物，从而大大提高了反转录起始步骤的效率。翻译。尽管S1与tmRNA的mRNA区结合，但我们发现SmpB和EF-Tu都与其受体臂区相互作用。在Ala-tRNA（Ala）的受体臂上也观察到了与SmpB和EF-Tu的相互作用，但其中的酰化效率被SmpB抑制而不是被刺激。因此，SmpB在其转译的连续步骤中可能充当tmRNA的tRNA样受体臂的重要调节剂。

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