Recognition of a start codon by the first aminoacyl-tRNA (Met-tRNAiMet) determines the reading frame of messenger RNA (mRNA) translation by the ribosome. In eukaryotes, the GTPase eIF5B collaborates in the correct positioning of Met tRNAiMet on the ribosome in the later stages of translation initiation, gating entrance into elongation. Leveraging the long residence time of eIF5B on the ribosome recently identified by single-molecule fluorescence measurements, we determined the cryoEM structure of the naturally long-lived ribosome complex with eIF5B and Met-tRNAiMet immediately before transition into elongation. The structure uncovered an unexpected, eukaryotic specific and dynamic fidelity checkpoint implemented by eIF5B in concert with components of the large ribosomal subunit.

中文翻译：

---

大的核糖体亚基，eIF5B，Met-tRNAiMet和mRNA共同完成了准确的启动。

第一个氨酰基-tRNA（Met-tRNAiMet）对起始密码子的识别决定了核糖体翻译信使RNA（mRNA）的阅读框架。在真核生物中，GTPase eIF5B在翻译起始的后期阶段协同作用，将Met tRNAiMet正确定位在核糖体上，从而控制进入延伸。利用最近通过单分子荧光测量确定的eIF5B在核糖体上的长停留时间，我们确定了在过渡到延伸之前，具有eIF5B和Met-tRNAiMet的天然长寿核糖体复合物的cryoEM结构。该结构揭示了eIF5B与大型核糖体亚基的组成部分共同实现的意想不到的，真核生物的特异性和动态保真检查点。