Multiple isoforms of the translation initiation factor eIF4GII are generated via use of alternative promoters, splice sites and a non-canonical initiation codon
Multiple isoforms of the translation initiation factor eIF4GII are generated via use of alternative promoters, splice sites and a non-canonical initiation codon
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DOI：
10.1042/bj20111765
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发表时间：
2012-11-15
影响因子：
4.1
通讯作者：
Morley, Simon J.
中科院分区：
文献类型：
--
作者：
Coldwell, Mark J.;Sack, Ulrike;Morley, Simon J.
在真核mRNA翻译的起始阶段，eIF 4G（真核起始因子4G）蛋白充当聚集点，用于将小核糖体亚基募集到mRNA。我们以前使用RNAi（RNA干扰）来减少内源性eIF 4GI蛋白的表达，导致蛋白合成速率降低和细胞形态改变。EIF 4G 1 cDNA的表达，编码不同的亚型（f-a），通过选择替代的起始密码子，拯救翻译到不同程度。此外，在eIF 4GI-敲低背景下eIF 4GII蛋白的过表达不能将翻译恢复到与eIF 4Glf/e同种型相同的程度，这表明由该蛋白支配的翻译事件是不同的。在本研究中，我们表明，多种异构体的eIF 4GII存在于哺乳动物细胞中，由多个启动子和选择性剪接事件，并确定了一个非经典的CUG起始密码子，延长eIF 4GII的N-末端。我们进一步表明，在eIF 4GI/eIF 4GII双敲低细胞中，我们的新型eIF 4GII同种型对翻译的拯救与用eIF 4GIf或eIF 4GIe观察到的一样稳健，并且比用原始eIF 4GII观察到的更稳健。由于新的eIF 4GII序列与eIF 4GI不同，这些数据表明eIF 4GII N-末端在起始因子组装中起替代作用。
During the initiation stage of eukaryotic mRNA translation, the eIF4G (eukaryotic initiation factor 4G) proteins act as an aggregation point for recruiting the small ribosomal subunit to an mRNA. We previously used RNAi (RNA interference) to reduce expression of endogenous eIF4GI proteins, resulting in reduced protein synthesis rates and alterations in the morphology of cells. Expression of EIF4G1 cDNAs, encoding different isoforms (f-a) which arise through selection of alternative initiation codons, rescued translation to different extents. Furthermore, overexpression of the eIF4GII paralogue in the eIF4GI-knockdown background was unable to restore translation to the same extent as eIF4GIf/e isoforms, suggesting that translation events governed by this protein are different. In the present study we show that multiple isoforms of eIF4GII exist in mammalian cells, arising from multiple promoters and alternative splicing events, and have identified a non-canonical CUG initiation codon which extends the eIF4GII N-terminus. We further show that the rescue of translation in eIF4GI/eIF4GII double-knockdown cells by our novel isoforms of eIF4GII is as robust as that observed with either eIF4GIf or eIF4GIe, and more than that observed with the original eIF4GII. As the novel eIF4GII sequence diverges from eIF4GI, these data suggest that the eIF4GII N-terminus plays an alternative role in initiation factor assembly.