Imataka H, Gradi A, Sonenberg N
Department of Biochemistry and McGill Cancer Centre, McGill University, Drummond Street 3655, Montreal, Quebec, Canada H3G 1Y6.
EMBO J. 1998 Dec 15;17(24):7480-9. doi: 10.1093/emboj/17.24.7480.
Most eukaryotic mRNAs possess a 5' cap and a 3' poly(A) tail, both of which are required for efficient translation. In yeast and plants, binding of eIF4G to poly(A)-binding protein (PABP) was implicated in poly(A)-dependent translation. In mammals, however, there has been no evidence that eIF4G binds PABP. Using 5' rapid amplification of cDNA, we have extended the known human eIF4GI open reading frame from the N-terminus by 156 amino acids. Co-immunoprecipitation experiments showed that the extended eIF4GI binds PABP, while the N-terminally truncated original eIF4GI cannot. Deletion analysis identified a 29 amino acid sequence in the new N-terminal region as the PABP-binding site. The 29 amino acid stretch is almost identical in eIF4GI and eIF4GII, and the full-length eIF4GII also binds PABP. As previously shown for yeast, human eIF4G binds to a fragment composed of RRM1 and RRM2 of PABP. In an in vitro translation system, an N-terminal fragment which includes the PABP-binding site inhibits poly(A)-dependent translation, but has no effect on translation of a deadenylated mRNA. These results indicate that, in addition to a recently identified mammalian PABP-binding protein, PAIP-1, eIF4G binds PABP and probably functions in poly(A)-dependent translation in mammalian cells.
大多数真核生物的信使核糖核酸（mRNA）都有一个5'帽和一个3'多聚腺苷酸（poly(A)）尾巴，这两者都是高效翻译所必需的。在酵母和植物中，真核起始因子4G（eIF4G）与多聚腺苷酸结合蛋白（PABP）的结合与多聚腺苷酸依赖性翻译有关。然而，在哺乳动物中，尚无证据表明eIF4G与PABP结合。利用5' cDNA快速扩增技术，我们将已知的人类eIF4GI开放阅读框从N端延伸了156个氨基酸。免疫共沉淀实验表明，延伸后的eIF4GI能结合PABP，而N端截短的原始eIF4GI则不能。缺失分析确定新N端区域中的一个29个氨基酸的序列为PABP结合位点。这个29个氨基酸的片段在eIF4GI和eIF4GII中几乎相同，全长的eIF4GII也能结合PABP。正如之前在酵母中所显示的，人类eIF4G与由PABP的RNA识别基序1（RRM1）和RRM2组成的片段结合。在体外翻译系统中，一个包含PABP结合位点的N端片段会抑制多聚腺苷酸依赖性翻译，但对去腺苷酸化mRNA的翻译没有影响。这些结果表明，除了最近发现的哺乳动物PABP结合蛋白PAIP-1外，eIF4G也能结合PABP，并且可能在哺乳动物细胞的多聚腺苷酸依赖性翻译中发挥作用。
