The human translation initiation multi-factor complex promotes methionyl-tRNAi binding to the 40S ribosomal subunit.
The human translation initiation multi-factor complex promotes methionyl-tRNAi binding to the 40S ribosomal subunit.
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DOI：
10.1093/nar/gkr772
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发表时间：
2012-01
影响因子：
14.9
通讯作者：
Hershey JW
中科院分区：
文献类型：
--
作者：
Sokabe M;Fraser CS;Hershey JW
Met-tRNAi向40 S核糖体亚基的递送被认为通过包含eIF 2、GTP和Met-tRNAi的三元复合物（TC）发生。我们已经从纯化的人蛋白质中产生了一种稳定的多因子复合物（MFC），包括eIF 1，eIF 2，eIF 3和eIF 5，类似于酵母和植物中报道的MFC。在HeLa细胞和兔网织红细胞中也检测到不含核糖体的人MFC，表明其存在于体内。在体外，MFC-GTP结合Met-tRNAi并以与TC相同的速率将tRNA递送至核糖体。然而，与eIF 2-GDP相比，MFC-GDP显示出对Met-tRNAi的亲和力大大降低，这表明MFC组分可能在AUG识别后从核糖体释放eIF 2-GDP中起作用。由于在细胞裂解物中检测到MFC-Met-tRNAi复合物，因此它可能与TC一起负责体内Met-tRNAi-40 S核糖体结合。然而，MFC蛋白组分也单独结合到40 S核糖体，产生了Met-tRNAi可能直接结合到这样的40 S-因子复合物的可能性。因此，三个不同的途径Met-tRNAi交付的40 S核糖体亚基被确定，但其中一个占主导地位，在体内仍有待阐明。
The delivery of Met-tRNAi to the 40S ribosomal subunit is thought to occur by way of a ternary complex (TC) comprising eIF2, GTP and Met-tRNAi. We have generated from purified human proteins a stable multifactor complex (MFC) comprising eIF1, eIF2, eIF3 and eIF5, similar to the MFC reported in yeast and plants. A human MFC free of the ribosome also is detected in HeLa cells and rabbit reticulocytes, indicating that it exists in vivo. In vitro, the MFC-GTP binds Met-tRNAi and delivers the tRNA to the ribosome at the same rate as the TC. However, MFC-GDP shows a greatly reduced affinity to Met-tRNAi compared to that for eIF2-GDP, suggesting that MFC components may play a role in the release of eIF2-GDP from the ribosome following AUG recognition. Since an MFC–Met-tRNAi complex is detected in cell lysates, it may be responsible for Met-tRNAi–40S ribosome binding in vivo, possibly together with the TC. However, the MFC protein components also bind individually to 40S ribosomes, creating the possibility that Met-tRNAi might bind directly to such 40S-factor complexes. Thus, three distinct pathways for Met-tRNAi delivery to the 40S ribosomal subunit are identified, but which one predominates in vivo remains to be elucidated.
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