SmpB contributes to reading frame selection in the translation of transfer-messenger RNA.
SmpB contributes to reading frame selection in the translation of transfer-messenger RNA.
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SMPB有助于转移通讯器RNA的翻译中的阅读框架选择。
DOI：
10.1016/j.jmb.2009.06.037
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发表时间：
2009-08-14
影响因子：
5.6
通讯作者：
Buskirk, Allen
中科院分区：
文献类型：
--
作者：
Watts, Talina;Cazier, DeAnna;Healey, David;Buskirk, Allen
转移信使RNA（Transfer-messenger RNA，tmRNA）首先作为tRNA，然后作为mRNA模板来拯救真细菌中停滞的核糖体。tmRNA与其蛋白伴侣SmpB一起进入停滞的核糖体，并将Ala残基转移到生长的多肽链上。然后发生了一个显著的步骤：核糖体离开停滞的mRNA，并以tmRNA为模板重新开始翻译，并添加一个短的肽标签，该标签注定要破坏中止的蛋白质。核糖体究竟是如何转换模板，在正确的阅读框架中恢复tmRNA的翻译，仍然是未知的。在tmRNA序列本身内，紧邻第一密码子上游的五个核苷酸（U85 AGUC）似乎指导框选择。特别地，保守的A86的突变导致在体外和体内的功能的严重丧失。A86 C突变导致翻译仅在+1框中恢复。已经在体外鉴定了该上游序列的几种候选结合伴侣。利用遗传选择技术对E.在大肠杆菌中，我们鉴定了在体内恢复A86 C tmRNA功能的SmpB蛋白的突变。SmpB突变体增加了正常阅读框中的标记，减少了+1框中的标记。这些结果表明，SmpB与tmRNA模板的上游序列功能性连接;两者都有助于tmRNA上的阅读框选择。
Transfer-messenger RNA (tmRNA) acts first as a tRNA and then as an mRNA template to rescue stalled ribosomes in eubacteria. Together with its protein partner, SmpB, tmRNA enters stalled ribosomes and transfers an Ala residue to the growing polypeptide chain. A remarkable step then occurs: the ribosome leaves the stalled mRNA and resumes translation using tmRNA as a template, adding a short peptide tag that destines the aborted protein for destruction. Exactly how the ribosome switches templates, resuming translation on tmRNA in the proper reading frame, remains unknown. Within the tmRNA sequence itself, five nucleotides (U85AGUC) immediately upstream of the first codon appear to direct frame selection. In particular, mutation of the conserved A86 results in severe loss of function both in vitro and in vivo. The A86C mutation causes translation to resume exclusively in the +1 frame. Several candidate binding partners for this upstream sequence have been identified in vitro. Using a genetic selection for tmRNA activity in E. coli, we identified mutations in the SmpB protein that restore the function of A86C tmRNA in vivo. The SmpB mutants increase tagging in the normal reading frame and reduce tagging in the +1 frame. These results demonstrate that SmpB is functionally linked with the sequence upstream of the tmRNA template; both contribute to reading frame selection on tmRNA.
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