The human translation initiation multi-factor complex promotes methionyl-tRNAi binding to the 40S ribosomal subunit

By M. Sokabe, C. Fraser, J. Hershey. 2011

90 citations recorded by the source corpus.

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.

Subfields: Molecular Biology

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In Molecular Biology

1. W. Merrick
2. G. Pavitt
3. A. Pisarev
4. V. Pisareva
5. A. Hinnebusch
6. C. Fraser
7. M. Sokabe
8. I. S. Fernández

Citations in the corpus

• eIF5 and eIF5B together stimulate 48S initiation complex formation during ribosomal scanning (2014, background): “In particular, the net of interactions within the MFC is different (4).”
• Structural Insights into the Mechanism of Scanning and Start Codon Recognition in Eukaryotic Translation Initiation. (2017, background): “The MFC likely participates in recruitment of TC to 40S subunits (Figure 1) in yeast [7,8] and also in mammals [10].”
• A structural inventory of native ribosomal ABCE1‐43S pre‐initiation complexes (2020, unknown): “Notably, eIF1A is the only factor that was not found to be pre-assembled in a 40S-free multi-factor complex (MFC) consisting of eIF1, eIF2-tRNA i -GTP, eIF3, and eIF5 in yeast (Asano et al , 2000; Zeman et al , 2019), plants, and mammals (Sokabe et al , 2012).”
• The scanning mechanism of eukaryotic translation initiation. (2014, background): “Although the stimulatory effect of mammalian MFC components on TC recruitment can occur without the preassembly of these components prior to 40S binding in vitro (63), it seems likely that the preformed MFC provides a major pathway to TC recruitment in vivo.”
• Protein Synthesis Initiation in Eukaryotic Cells. (2018, background): “There is evidence that in plants the affinities of these MFC components for each other is enhanced by phosphorylation (Dennis et al. 2009), but whether phosphorylation similarly affects human MFC interaction affinities has not yet been evaluated (Sokabe et al. 2012).”