Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991, Russia.
School of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, 119234, Russia.
Sci Rep. 2016 Nov 28;6:37905. doi: 10.1038/srep37905.
mRNAs lacking 5' untranslated regions (leaderless mRNAs) are molecular relics of an ancient translation initiation pathway. Nevertheless, they still represent a significant portion of transcriptome in some taxons, including a number of eukaryotic species. In bacteria and archaea, the leaderless mRNAs can bind non-dissociated 70 S ribosomes and initiate translation without protein initiation factors involved. Here we use the Fleeting mRNA Transfection technique (FLERT) to show that translation of a leaderless reporter mRNA is resistant to conditions when eIF2 and eIF4F, two key eukaryotic translation initiation factors, are inactivated in mammalian cells. We report an unconventional translation initiation pathway utilized by the leaderless mRNA in vitro, in addition to the previously described 80S-, eIF2-, or eIF2D-mediated modes. This mechanism is a bacterial-like eIF5B/IF2-assisted initiation that has only been reported for hepatitis C virus-like internal ribosome entry sites (IRESs). Therefore, the leaderless mRNA is able to take any of four different translation initiation pathways in eukaryotes.
缺乏 5' 非翻译区（无帽 mRNA）的 mRNAs 是一种古老翻译起始途径的分子遗迹。然而，它们在一些分类群中仍然代表着转录组的重要部分，包括一些真核生物。在细菌和古菌中，无帽 mRNAs 可以与非解离的 70S 核糖体结合，并在不涉及起始蛋白因子的情况下起始翻译。在这里，我们使用短暂 mRNA 转染技术 (FLERT) 表明，在哺乳动物细胞中失活 eIF2 和 eIF4F（两种关键的真核翻译起始因子）的情况下，无帽报告 mRNA 的翻译具有抗性。我们报告了无帽 mRNA 在体外除了先前描述的 80S-、eIF2-或 eIF2D 介导的模式之外，还利用了一种非常规的翻译起始途径。这种机制是一种类似于细菌的 eIF5B/IF2 辅助起始，仅在丙型肝炎病毒样内部核糖体进入位点 (IRES) 中报道过。因此，无帽 mRNA 能够在真核生物中采取四种不同的翻译起始途径之一。
