des Georges Amedee, Dhote Vidya, Kuhn Lauriane, Hellen Christopher U T, Pestova Tatyana V, Frank Joachim, Hashem Yaser
HHMI, Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA.
Department of Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York 11203, USA.
Nature. 2015 Sep 24;525(7570):491-5. doi: 10.1038/nature14891. Epub 2015 Sep 7.
During eukaryotic translation initiation, 43S complexes, comprising a 40S ribosomal subunit, initiator transfer RNA and initiation factors (eIF) 2, 3, 1 and 1A, attach to the 5'-terminal region of messenger RNA and scan along it to the initiation codon. Scanning on structured mRNAs also requires the DExH-box protein DHX29. Mammalian eIF3 contains 13 subunits and participates in nearly all steps of translation initiation. Eight subunits having PCI (proteasome, COP9 signalosome, eIF3) or MPN (Mpr1, Pad1, amino-terminal) domains constitute the structural core of eIF3, to which five peripheral subunits are flexibly linked. Here we present a cryo-electron microscopy structure of eIF3 in the context of the DHX29-bound 43S complex, showing the PCI/MPN core at ∼6 Å resolution. It reveals the organization of the individual subunits and their interactions with components of the 43S complex. We were able to build near-complete polyalanine-level models of the eIF3 PCI/MPN core and of two peripheral subunits. The implications for understanding mRNA ribosomal attachment and scanning are discussed.
在真核生物翻译起始过程中，由40S核糖体亚基、起始转运RNA和起始因子（eIF）2、3、1及1A组成的43S复合物附着于信使RNA的5'末端区域，并沿其扫描至起始密码子。在结构化信使RNA上进行扫描还需要DExH盒蛋白DHX29。哺乳动物的eIF3含有13个亚基，几乎参与翻译起始的所有步骤。八个具有PCI（蛋白酶体、COP9信号体、eIF3）或MPN（Mpr1、Pad1、氨基末端）结构域的亚基构成了eIF3的结构核心，五个外围亚基与之灵活相连。在此，我们展示了与DHX29结合的43S复合物背景下eIF3的冷冻电镜结构，以约6 Å的分辨率显示了PCI/MPN核心。它揭示了各个亚基的组织方式及其与43S复合物各组分的相互作用。我们能够构建eIF3的PCI/MPN核心以及两个外围亚基的近乎完整的聚丙氨酸水平模型。文中讨论了这对于理解信使RNA与核糖体附着及扫描的意义。
