Structural basis for stop codon recognition in eukaryotes.
Structural basis for stop codon recognition in eukaryotes.
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DOI：
10.1038/nature14896
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发表时间：
2015-08-27
期刊：
影响因子：
64.8
通讯作者：
Ramakrishnan V
中科院分区：
文献类型：
--
作者：
Brown A;Shao S;Murray J;Hegde RS;Ramakrishnan V
蛋白质合成的终止发生在翻译核糖体遇到三个普遍保守的终止密码子之一时：UGA，UAA或UAG。释放因子识别核糖体A位点中的终止密码子以介导新生链的释放和核糖体的再循环。细菌使用两种单独的释放因子来解码终止密码子，所述释放因子对第二和第三碱基具有不同的特异性。相比之下，真核生物依赖于进化无关的全能释放因子（eRF 1）来识别所有三个终止密码子。终止密码子相对于有义密码子的eRF 1区分的分子基础尚不清楚。在这里，我们提出了电子冷冻显微镜（cryo-EM）结构在3.5 - 3.8 μ m的分辨率哺乳动物核糖体复合物含有eRF 1相互作用的三个终止密码子在A网站。eRF 1的结合翻转18 S rRNA的核苷酸A1825，使其堆叠在第二和第三终止密码子碱基上。这种构型将第四个位置的碱基拉入A位点，在那里它通过与18 S rRNA的G626堆叠而稳定。因此，eRF 1利用了在tRNA选择过程中也使用的两个rRNA核苷酸来驱动mRNA压缩。终止密码子在这种紧凑的mRNA构象中通过与限制碱基身份的必需eRF 1残基的氢键网络而受到青睐。这些结果提供了一个真核生物终止密码子识别的分子框架，并对未来的经典和过早的翻译终止机制的研究具有启示意义。
Termination of protein synthesis occurs when a translating ribosome encounters one of three universally conserved stop codons: UGA, UAA, or UAG. Release factors recognise stop codons in the ribosomal A site to mediate release of the nascent chain and recycling of the ribosome. Bacteria decode stop codons using two separate release factors with differing specificities for the second and third bases. By contrast, eukaryotes rely on an evolutionarily unrelated omnipotent release factor (eRF1) to recognise all three stop codons. The molecular basis of eRF1 discrimination for stop codons over sense codons is not known. Here, we present electron cryo-microscopy (cryo-EM) structures at 3.5 – 3.8 Å resolution of mammalian ribosomal complexes containing eRF1 interacting with each of the three stop codons in the A site. Binding of eRF1 flips nucleotide A1825 of 18S rRNA so that it stacks on the second and third stop codon bases. This configuration pulls the fourth position base into the A site, where it is stabilised by stacking against G626 of 18S rRNA. Thus, eRF1 exploits two rRNA nucleotides also used during tRNA selection to drive mRNA compaction. Stop codons are favoured in this compacted mRNA conformation by a hydrogen-bonding network with essential eRF1 residues that constrains the identity of the bases. These results provide a molecular framework for eukaryotic stop codon recognition and have implications for future studies on the mechanisms of canonical and premature translation termination.