Belozersky Institute of Physico-Chemical Biology, Moscow State University, Building A, Moscow 119992, Russia.
J Mol Biol. 2011 Oct 14;413(1):106-14. doi: 10.1016/j.jmb.2011.08.026. Epub 2011 Aug 23.
Heterotrimeric translation initiation factor (IF) a/eIF2 (archaeal/eukaryotic IF 2) is present in both Eukarya and Archaea. Despite strong structural similarity between a/eIF2 orthologs from the two domains of life, their functional relationship is obscure. Here, we show that aIF2 from Sulfolobus solfataricus can substitute for its mammalian counterpart in the reconstitution of eukaryotic 48S initiation complexes from purified components. aIF2 is able to correctly place the initiator Met-tRNA(i) into the P-site of the 40S ribosomal subunit and accompany the entire set of eukaryotic translation IFs in the process of cap-dependent scanning and AUG codon selection. However, it seems to be unable to participate in the following step of ribosomal subunit joining. In accordance with this, aIF2 inhibits rather than stimulates protein synthesis in mammalian cell-free system. The ability of recombinant aIF2 protein to direct ribosomal scanning suggests that some archaeal mRNAs may utilize this mechanism during translation initiation.
异三聚体翻译起始因子 (IF) a/eIF2（古菌/真核 IF2）存在于真核生物和古菌中。尽管生命两个领域的 a/eIF2 同源物在结构上具有很强的相似性，但它们的功能关系尚不清楚。在这里，我们表明来自 Sulfolobus solfataricus 的 aIF2 可以替代其哺乳动物对应物，用于从纯化的成分中重建真核 48S 起始复合物。aIF2 能够将起始 Met-tRNA(i) 正确地放置在 40S 核糖体亚基的 P 位，并在帽依赖性扫描和 AUG 密码子选择过程中伴随整套真核翻译 IF。然而，它似乎无法参与核糖体亚基结合的后续步骤。与此一致的是，aIF2 在哺乳动物无细胞系统中抑制而不是刺激蛋白质合成。重组 aIF2 蛋白引导核糖体扫描的能力表明，一些古菌 mRNA 在翻译起始时可能利用这种机制。
