Department of Biology, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, ETH Zurich, CH-8093 Zurich, Switzerland.
Department of Biology, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, ETH Zurich, CH-8093 Zurich, Switzerland.
Mol Cell. 2017 Aug 3;67(3):447-456.e7. doi: 10.1016/j.molcel.2017.06.032. Epub 2017 Jul 18.
After having translated short upstream open reading frames, ribosomes can re-initiate translation on the same mRNA. This process, referred to as re-initiation, controls the translation of a large fraction of mammalian cellular mRNAs, many of which are important in cancer. Key ribosomal binding proteins involved in re-initiation are the eukaryotic translation initiation factor 2D (eIF2D) or the homologous complex of MCT-1/DENR. We determined the structures of these factors bound to the human 40S ribosomal subunit in complex with initiator tRNA positioned on an mRNA start codon in the P-site using a combination of cryoelectron microscopy and X-ray crystallography. The structures, supported by biochemical experiments, reveal how eIF2D emulates the function of several canonical translation initiation factors by using three independent, flexibly connected RNA binding domains to simultaneously monitor codon-anticodon interactions in the ribosomal P-site and position the initiator tRNA.
核糖体在翻译完短的上游开放阅读框后，可以在同一 mRNA 上重新起始翻译。这个过程被称为重新起始，它控制着哺乳动物细胞中很大一部分 mRNA 的翻译，其中许多在癌症中很重要。重新起始涉及的关键核糖体结合蛋白是真核翻译起始因子 2D（eIF2D）或 MCT-1/DENR 同源复合物。我们使用冷冻电子显微镜和 X 射线晶体学的组合，确定了这些因子与结合在 P 位上的起始 tRNA 与位于 mRNA 起始密码子上的人 40S 核糖体亚基复合物的结构。这些结构得到了生化实验的支持，揭示了 eIF2D 如何通过使用三个独立的、灵活连接的 RNA 结合结构域来模拟几个典型的翻译起始因子的功能，从而同时监测核糖体 P 位上的密码子-反密码子相互作用，并定位起始 tRNA。
