Initiation Factors in Eukaryotes


Initiation factors are those proteins that facilitate the assembly of the initiator tRNA, mRNA and ribosomes into an initiation complex. This assembly correctly matches the AUG start codon of the mRNA with the anticodon of the initiator tRNA in the ribosomal P site and thereby determines the translational reading frame.

Keywords: protein synthesis; initiation factors; scanning; helicase; ribosomes; tRNA; mRNA; ATP; GTP

Figure 1.

A model pathway for the formation of an 80S initiation complex. The initiation factors are identified by their standard names; however, once bound to the ribosome, they are indicated by their number in a box. The ternary complex of eIF2•GTP•Met‐tRNAi, is indicated by 3° in a box. Note that while all of the factors bind to the 40S subunit, only eIF2 (as the ternary complex), eIF3, eIF6 and eIF1A bind stably enough to survive isolation by sucrose gradients, the major technique used to establish the pathway. The other factors bind less tightly and with poorer stoichiometry.



Asano K, Vornlocher H‐P, Richter‐Cook NJ, Merrick WC, Hinnebusch AG and Hershey JWB (1997) Structure of cDNAs encoding human eukaryotic initiation factor 3 subunits. Journal of Biological Chemistry 272: 27042–27052.

Clark BFC, Grunberg‐Manago M, Gupta N et al. (1996) Prokaryotic and eukaryotic translation factors. Biochimie 78: 1119–1122.

Cigan AM, Feng L and Donahue TF (1988) tRNAi(met) functions in directing the scanning ribosome to the start site of translation. Science 242: 93–97.

Dholakia JN and Wahba AJ (1989) Mechanism of the nucleotide exchange reaction in eukaryotic polypeptide chain initiation. Journal of Biological Chemistry 264: 546–550.

Godefroy‐Colburn T and Thach RE (1981) The role of mRNA competition in regulating translation: IV. The kinetic model. Journal of Biological Chemistry 256: 11762–11773.

Merrick WC and Hershey JWB (1996) The pathway and mechanism of eukaryotic protein synthesis. In: Hershey JWB et al. (eds) Translational Control, pp. 32–69. Cold Spring Harbor, NY: Cold Spring Harbor Press.

Park HP, Wolff EC and Folk JE (1993) Hypusine: its post‐translational formation in eukaryotic initiation factor 5A and its potential role in cellular regulation. BioFactors 4: 95–104.

Pause A and Sonenberg N (1992) Mutational analysis of a DEAD box helicase: the mammalian translation initiation factor eIF‐4A. EMBO Journal 11: 2643–2654.

Further Reading

Kozak M (1989) The scanning model for translation: an update. Journal of Cellular Biology 108: 229–241.

Hershey JWB (1991) Translational control in mammalian cells. Annual Reviews of Biochemistry 60: 717–755.

Merrick WC (1992) Mechanism and regulation of eukaryotic protein synthesis. Microbiological Reviews 56: 291–315.

Pain VM (1996) Initiation of protein synthesis in eukaryotic cells. European Journal of Biochemistry 236: 747–771.

Sachs AB, Sarnow P and Hentze MW (1997) Starting at the beginning, middle and end: translation initiation in eukaryotes. Cell 89: 831–838.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Merrick, William C(Apr 2001) Initiation Factors in Eukaryotes. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0000545]