CNRS, Architecture et Réactivité de l'ARN UPR9002, Université de Strasbourg, 67084 Strasbourg, France.
CNRS, Architecture et Réactivité de l'ARN UPR9002, Université de Strasbourg, 67084 Strasbourg, France.
Mol Cell. 2016 Jul 21;63(2):206-217. doi: 10.1016/j.molcel.2016.05.033. Epub 2016 Jun 30.
mRNA translation initiation in eukaryotes requires the cooperation of a dozen eukaryotic initiation factors (eIFs) forming several complexes, which leads to mRNA attachment to the small ribosomal 40S subunit, mRNA scanning for start codon, and accommodation of initiator tRNA at the 40S P site. eIF3, composed of 13 subunits, 8 core (a, c, e, f, h, l, k, and m) and 5 peripheral (b, d, g, i, and j), plays a central role during this process. Here we report a cryo-electron microscopy structure of a mammalian 48S initiation complex at 5.8 Å resolution. It shows the relocation of subunits eIF3i and eIF3g to the 40S intersubunit face on the GTPase binding site, at a late stage in initiation. On the basis of a previous study, we demonstrate the relocation of eIF3b to the 40S intersubunit face, binding below the eIF2-Met-tRNAi(Met) ternary complex upon mRNA attachment. Our analysis reveals the deep rearrangement of eIF3 and unravels the molecular mechanism underlying eIF3 function in mRNA scanning and timing of ribosomal subunit joining.
真核生物的 mRNA 翻译起始需要十几个真核起始因子 (eIFs) 形成几个复合物，这些复合物导致 mRNA 与小核糖体 40S 亚基结合，mRNA 扫描起始密码子，并使起始 tRNA 适应 40S P 位。由 13 个亚基组成的 eIF3，包括 8 个核心 (a、c、e、f、h、l、k 和 m) 和 5 个外周 (b、d、g、i 和 j)，在这个过程中起着核心作用。在这里，我们报道了一个哺乳动物 48S 起始复合物在 5.8Å分辨率的低温电子显微镜结构。它显示了在起始的晚期，eIF3i 和 eIF3g 亚基重新定位到 40S 亚基间表面的 GTPase 结合位点上。基于之前的一项研究，我们证明了 eIF3b 重新定位到 40S 亚基间表面，在 mRNA 结合后结合在 eIF2-Met-tRNAi(Met)三元复合物的下方。我们的分析揭示了 eIF3 的深刻重排，并阐明了 eIF3 在 mRNA 扫描和核糖体亚基结合时机中的功能的分子机制。
