Eukaryotic elongation factors

Elongation factors Eukaryotic elongation factors (eEFs) Prokaryotic elongation factors (EFs)... 

Shastry, M., Nielsen, J., Ku, T., Hsu, M. J., Liberator, P., Anderson, J., Schmatz, D., and Justice, M. C. (2001). Species-specific inhibition of fungal protein synthesis by sordarin Identification of a sordarin-specificity region in eukaryotic elongation factor 2. Microbiology 147, 383-390. 

ARF, ADP-ribosylation factor EFTU, eukaryotic elongation factor. 

A third type of bacterial toxin, diphtheria toxin, catalyzes the ADP-ribosylation of eukaryotic elongation factor (EFTU), a type of small G protein involved in protein synthesis (Table 19-2). The functional activity of the elongation factor is inhibitedby this reaction. Finally, a botulinum toxin ADP-ribosylates and disrupts the function of the small G protein Rho, which appears to be involved in assembly and rearrangement of the actin cytoskeleton (Table 19-2). These toxins maybe involved in neuropathy (see Ch. 36) and membrane trafficking (see Ch. 9). 

Histones and nonhistone nuclear proteins Ribosomal protein S6 elF (eukaryotic initiation factor) eEF (eukaryotic elongation factor)... 

EFTU eukaryotic elongation factor GRK G protein receptor kinase... 

Upon being formed by the aaRSs, aa-tRNAs are trapped by the elongation factor EF-Tu in prokaryotes and EF-IA in eukaryotes and archaea and carried to the ribosome where they are used for elongation of the... 

In eukaryotic cells, elongation factor-2 (eEF-2) used in translocation is inactivated through ADP-ribosylation by Pseudomonas and Diphtheria toxins. 

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... 

Ribosome recycling factor (RRF) and elongation factor-G (EF-G) are required to recycle the prokaryotic ribosome back to a new round of initiation after termination (Nakamura and Ito 2003). No recycling factor has been identified so far in the cytoplasm of eukaryotic cells. To explain this difference it has been postulated that eukaryotic eRF3 has a dual function ... 

The elongation cycle in eukaryotes is quite similar to that in prokaryotes. Three eukaryotic elongation factors (eEFla, eEFljSy, and eEF2) have functions analogous to those of the bacterial elongation factors (EF-Tu, EF-Ts, and EF-G, respectively). Eukaryotic ribosomes do not have an E site uncharged tRNAs are expelled directly from the P site. 

Several other inhibitors of protein synthesis are notable because of their toxicity to humans and other mammals. Diphtheria toxin (Mr 58,330) catalyzes the ADP-ribosylation of a diphthamide (a modified histidine) residue of eukaryotic elongation factor eEF2, thereby inactivating it. Ricin (Afr 29,895), an extremely toxic protein of the castor bean, inactivates the 60S subunit of eukaryotic ribosomes by depurinating a specific adenosine in 23S rRNA. 

Inactivates the eukaryotic elongation factor, eEF-2, thus preventing translocation,... 

At the conclusion of the initiation process, the ribosome is poised to translate the reading frame associated with the initiator codon. The translation of the contiguous codons in mRNA is accomplished by the sequential repetition of three reactions with each amino acid. These three reactions of elongation are similar in both prokaryotic and eukaryotic systems two of them require nonribosomal proteins known as elongation factors (EF). Interestingly, the actual formation of the peptide bond does not require a factor and is the only reaction of protein synthesis catalyzed by the ribosome itself. 

The structural differences between bacterial and eukaryotic elongation factors are highlighted by the selective action that diphtheria has on eukaryotic systems (box 29B). 

Elongation in eukaryotes requires three eukaryotic initiation factors that have similar functions to the corresponding prokaryotic proteins. 

The elongation stage of translation in eukaryotes requires three elongation factors, eEFla, eEFI[3y and eEF2, which have similar functions to their prokaryotic counterparts EF-Tu, EF-Ts and EF-G (see Table 1). 

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