The eukaryotic initiation factor 3 (eIF3) complex is involved in every step of translation initiation, but there is limited understanding of its molecular functions. Here, we present a single particle electron cryomicroscopy (cryo-EM) reconstruction of yeast 48S ribosomal preinitiation complex (PIC) in an open conformation conducive to scanning, with core subunit eIF3b bound on the 40S interface near the decoding center in contact with the ternary complex eIF2·GTP·initiator tRNA. eIF3b is relocated together with eIF3i from their solvent interface locations observed in other PIC structures, with eIF3i lacking 40S contacts. Re-processing of micrographs of our previous 48S PIC in a closed state also suggests relocation of the entire eIF3b-3i-3g-3a-Cter module during the course of initiation. Genetic analysis indicates that high fidelity initiation depends on eIF3b interactions at the 40S subunit interface that promote the closed PIC conformation, or facilitate the relocation of eIF3b/eIF3i to the solvent interface, on start codon selection.

中文翻译：

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翻译起始期间eIF3结构域的大规模移动调节起始密码子选择

真核起始因子 3 (eIF3) 复合物参与翻译起始的每一步，但对其分子功能的了解有限。在这里，我们提出了酵母 48S 核糖体预起始复合物 (PIC) 的单粒子电子低温显微镜 (cryo-EM) 重建，其具有有利于扫描的开放构象，核心亚基 eIF3b 结合在解码中心附近的 40S 界面上，与三元相接触复杂的eIF2·GTP·启动子tRNA。eIF3b 与 eIF3i 一起从在其他 PIC 结构中观察到的溶剂界面位置重新定位，eIF3i 缺少 40S 接触。在关闭状态下重新处理我们之前的 48S PIC 的显微照片也表明在启动过程中重新定位整个 eIF3b-3i-3g-3a-Cter 模块。