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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

Eukaryotic Initiation Factors (eIF) and Functions

eukaryotic initiation factors
List of Eukaryotic  Initiation Factors
(Source: Nature)
 
 Initiation of Protein synthesis in Eukayotes

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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