Functions of Eukaryotic Initiation Factors (eIF)

Initiation Factors (IF): Proteins that are required for the initiation of a new polypeptide chain.

Prokaryotic Initiation Factors (PIF): PIF-1 , PIF-2 , PIF-3.

Archaeal Initiation Factors (aIF): aIF1 , aIF2 , aIF5 , aIF6.

Eukaryotic Initiation Factors (eIF): In Eukaryotes 10 initiation factors have been identified in red blood cells (reticulocytes). They are named by putting a prefix ‘e’ to signify their eukaryotic origin. These factors are eIF1, eIF2, eIF3, eIF4 , eIF5, eIF6 ,eIF4B, eIF4C, eIF4D, eIF4F.

Eukaryotic Initiation Factors (eIF) and Functions

List of Eukaryotic  Initiation Factors
(Source: Nature)

 

Simplified (points to remember)

Eukaryotic Initiation Factors (eIF)	Structure   & Mass (Dalton)	Functions
eIF1	Monomer 15,000	Assists mRNA binding
eIF2	Trimer contains three chains: αchain 35,000	Binding to Met-tRNA Binds to GTP
	β  chain 38,000	Recycling factor
	γ  chain 55,000	Binding to Met-tRNA.
eIF3	Multimer 7,5,00,000	Binding mRNA
eIF4A	Multimer 15,000	Assists mRNA binding (also binds ATP).
eIF4B	Monomer 15,000	Assists mRNA binding and unbinding.
eIF4C	Monomer 15,000	Binding 60S subunit.
eIF4D	Monomer
eIF4E	Monomer 15,000	Binding 60S subunit to 40s subunit and mRNA
eIF4G
eIF4H	Monomer
eIF4F	Multimer 2,00,000	Binding mRNA 5’end; unwinding.
eIF5	Monomer 1,50,000	Releasing eIF2 and eIF3.
eIF6	Monomer 23,000	Prevents 40S-60S joining.

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• List of Eukaryotic initiation factors