Translation protein factors

Although rRNA is paramount in the process of translation, protein factors also are required for the efficient synthesis of a protein. Protein factors participate in the initiation, elongation, and termination of protein synthesis. P-loop NTPases of the G-protein family play particularly important roles. Recall that these proteins serve as molecular switches as they cycle between a GTP-bound form and a GDP-bound form (Section 15.1.2). 

Danaie, P., Wittmer, B., Altmann, M., and Trachsel, H. (1995). Isolation of a protein complex containing translation initiation factor Prtl from Saccharomyces cerevisiae. J. Biol. Ghent. 270, 4288-4292. 

Naranda, T., MacMillan, S. E., and Hershey, J. W. B. (1994). Purified yeast translational initiation factor eIF-3 is an RNA-binding protein complex that contains the PRT1 protein. J. Biol. Chem. 269, 32286—32292. 

The discovery of Green Fluorescent Protein (GFP) and the development of technology that allows specific proteins to be tagged with GFP has fundamentally altered the types of question that can be asked using cell biological methods. It is now possible not only to study where a protein is within a cell, but also feasible to study the precise dynamics of protein movement within living cells. We have exploited these technical developments and applied them to the study of translation initiation factors in yeast, focusing particularly on the... 

Genes of interest can be tagged at either the N or C terminal end. The decision to tag a protein at either the N or the C terminal depends upon the properties of the protein of interest. In our case, all the eukaryotic translation initiation factors were tagged C terminally to allow the endogenous promoter to influence the expression of the tagged protein. 

In studying the localization of eukaryotic translation initiation factors, we made use of the FR AP technique to determine whether the localized regions of eIF2/eIF2B represented dynamic centers of these proteins (Campbell et ah, 2005). 

Srivastava, S. P., Kumar, K. U., and Kaufman, R. J. (1998). Phosphorylation of eukaryotic translation initiation factor 2 mediates apoptosis in response to activation of the double-stranded RNA-dependent protein kinase. J. Biol. Chem. 273, 2416—2423. 

Kahvejian, A., Svitkin, Y. V., Sukarieh, R., M Boutchou, M. N., and Sonenberg, N. (2005). Mammalian poly(A)-binding protein is a eukaryotic translation initiation factor, which acts via multiple mechanisms. Genes Dev. 19, 104—113. 

Mader, S., Lee, H., Pause, A., and Sonenberg, N. (1995). The translation initiation factor eIF-4E binds to a common motif shared by the translation factor eIF-4gamma and the translational repressors 4E-binding proteins. Mol. Cell. Biol. 15, 4990-4997. 

The cap-binding protein eIF4E promotes folding of a functional domain of yeast translation initiation factor eIF4Gl.J. Biol. Chem. 274, 21297—21304. 

Tarun, S. J. J., and Sachs, A. B. (1996). Association of the yeast poly(A) tail binding protein with translation initiation factor eIF4G. EMBOJ. 15, 7168—7177. 

In the EPR of mammalian cells, we do not see much in addition to the signals from the respiratory complexes. The enzyme aconitase from the citric-acid cycle can be detected, and also the protein cytoplasmic aconitase, later identified as the mRNA translation regulatory factor iron regulatory protein IRP-1, which actually started its career in biochemistry as an EPR signal that could not be assigned to the respiratory chain (Kennedy et al. 1992). 

PSI] is the prion of Sup35p, a translation termination factor (Ter-Avanesyan et al., 1994 Wickner, 1994). Conversion of wild-type yeast cells to the infected state results in reduction of the termination activity and, consequendy, to a nonsense suppression phenotype. This property can be used to detect [PSI] by genetic selection (Fig. 2). Sup35p is an essential gene whose knockout leads to cell death. Therefore, it appears that the [PSI] condition corresponds to only partial inactivation of Sup35p and enough of the normal protein is left to avert cell death. 

Gribskov, M. (1992). Translational initiation factors IF-1 and eIF-2 alpha share an RNA-binding motif with prokaryotic ribosomal protein SI and polynucleotide phosphoryl-ase. Gene 119, 107-111. 

Tan, N. G., et al., Human homologue of ariadne promotes the ubiquitylation of translation initiation factor 4E homologous protein, 4EHP. FEES Lett, 2003, 554(3), 501-4. 

The CSN3 subunit interacts with IKKy, a component of the IsrB-kinase complex controlling NF-kB activity [32]. Additionally, it is the binding site for the CSN-associated kinases CK2 and PKD [31]. The subunit of the translation-initiation factor 3 complex, Int6/eIF3e, and the ubiquitin-conjugating enzyme variant, COPIO, have been identified as other cellular interactors [33, 34]. Also the HIV-1 Tat protein interacts with CSN 3 (our unpublished data). 

Answer C. eIF-2 designates a protein factor of the initiation phase in eukaryotic translation. The only event listed that would occur during this phase is placement of initiator tRNA in the P-site. 

Abbreviations aa-tRNA Amino-acyl tRNA eLF Eukaryotic translation initiation factor IF Prokaryotic translation initiation factor eEF Eukaryotic translation elongation factor EF Prokaryotic translation elongation factor eRF Eukaryotic translation termination factor (release factor) RF Prokaryotic translation release factor RRF Ribosome recycling factor Rps Protein of the prokaryotic small ribosomal subunit Rpl Protein of the eukaryotic large ribosomal subunit S Protein of the prokaryotic small ribosomal subunit L Protein of the prokaryotic large ribosomal subunit PTC Peptidyl transferase center RNC Ribosome-nascent chain-mRNA complex ram Ribosomal ambiguity mutation RAC Ribosome-associated complex NMD Nonsense-mediated mRNA decay... 

Accurate selection of translation termination factors to ribosomes containing a stop codon in the A-site is less well understood. A picture is only beginning to emerge as the bacterial 708 ribosome and class I release factor RF2 atomic models have recently been fitted into cryo-EM stmctures. Via multiple interactions RF2 connects the ribosomal decoding site with the PTC and functionally mimics a tRNA molecule in the A-site. In the complex RF2 is close to helices 18, 44, and 31 of the 168 rRNA, small subunit ribosomal protein 812, helices 69, 71, 89, and 92 of the 238 rRNA, the L7/L12 stalk, and protein LI 1 of the large subunit (Arkov et al. 2000 Klaholz et al. 2003 Rawat et al. 2003). The L7/L12 stalk inter-... 

Proteins interacting with translation termination factors affect the fidelity of translation termination... 

Recent studies have shown that proteins interacting with the release factors can modulate the efficiency of stop codon readthrough. Physical and functional interaction with the translation termination factors was demonstrated for different components of the translational machinery. 

Aminoglycoside effects on mutants in translation termination factors and proteins interacting with the ribosome... 

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