Imataka H, Sonenberg N
Department of Biochemistry and McGill Cancer Centre, McGill University, Montreal, Quebec, Canada.
Mol Cell Biol. 1997 Dec;17(12):6940-7. doi: 10.1128/MCB.17.12.6940.
Mammalian translation initiation factor 4F (eIF4F) consists of three subunits, eIF4A, eIF4E, and eIF4G. eIF4G interacts directly with both eIF4A and eIF4E. The binding site for eIF4E is contained in the amino-terminal third of eIF4G, while the binding site for eIF4A was mapped to the carboxy-terminal third of the molecule. Here we show that human eIF4G possesses two separate eIF4A binding domains in the middle third (amino acids [aa] 478 to 883) and carboxy-terminal third (aa 884 to 1404) of the molecule. The amino acid sequence of the middle portion of eIF4G is well conserved between yeasts and humans. We show that mutations of conserved amino acid stretches in the middle domain abolish or reduce eIF4A binding as well as eIF3 binding. In addition, a separate and nonoverlapping eIF4A binding domain exists in the carboxy-terminal third (aa 1045 to 1404) of eIF4G, which is not present in yeast. The C-terminal two-thirds region (aa 457 to 1404) of eIF4G, containing both eIF4A binding sites, is required for stimulating translation. Neither one of the eIF4A binding domains alone activates translation. In contrast to eIF4G, human p97, a translation inhibitor with homology to eIF4G, binds eIF4A only through the amino-terminal proximal region, which is homologous to the middle domain of eIF4G.
哺乳动物翻译起始因子4F(eIF4F)由三个亚基组成,即eIF4A、eIF4E和eIF4G。eIF4G直接与eIF4A和eIF4E相互作用。eIF4E的结合位点位于eIF4G氨基末端的三分之一区域,而eIF4A的结合位点则定位在该分子羧基末端的三分之一区域。在此我们表明,人类eIF4G在该分子中间三分之一区域(氨基酸[aa]478至883)和羧基末端三分之一区域(aa 884至1404)拥有两个独立的eIF4A结合结构域。eIF4G中间部分的氨基酸序列在酵母和人类之间高度保守。我们发现,中间结构域中保守氨基酸片段的突变会消除或减少eIF4A结合以及eIF3结合。此外,在eIF4G羧基末端三分之一区域(aa 1045至1404)存在一个单独且不重叠的eIF4A结合结构域,该结构域在酵母中不存在。eIF4G的羧基末端三分之二区域(aa 457至1404)包含两个eIF4A结合位点,是刺激翻译所必需的。单独的任何一个eIF4A结合结构域均不能激活翻译。与eIF4G不同,人类p97是一种与eIF4G具有同源性且为翻译抑制剂的蛋白,它仅通过与eIF4G中间结构域同源的氨基末端近端区域结合eIF4A。