Factor

Mol.wt (KD)

Function (s)

eIF-1

15

15kd, monomer; it is a pleotropic factor or multifunctional factor acts at many steps in initiation, it assists in mRNA binding, and activates chain initiation by 20%.

eIF1A(eIF4C)

17

Helps in met-i.tRNA and mRNA binding to 40s

eIF-2A-abc

125 (130) (Trimer: alpha(36),beta(50), gamma(55)

Activated eIF2A (GTP) binds to met-i.tRNA, Helps in initiator tRNA complex binding to 40s ribosome.  It is similar to prokaryotic IF-2 in function.

eIF-2B (GEF)

a-26, b-39, y-58, d67, e-82=270

Binds to GTP, acts as GEF (GTP Exchange Factor)-[eIf2A-GDP-GEF-eIF2A-GTP]

eIF2

94

Stabilize ternary complex

eIF-3

550-737kd (8-10) subunits 

Similar to PKs IF-3 in function, it is an anti-dimer factor, itself binds to 40s and prevents 60s subunit association (an anti-association factor), but activates 40 ribosome, stimulate mRNA binding to 40s Ribosome-like eIF6

eIF3A helicase (eiF6)

46

Ribosome dissociation

eIF4F

IF4A.4E,4G1/G3 4E interacts with its partner prots-4EBP1,4EBP2,4EBP3.

eIF4A

44-46

Binds mRNA at 5’ end,  helicase has DEAD box sequence, scans 5’UTR to remove sec. structures

eIF4-B

65-80kd

Monomer; assists 4-A in binding to mRNA and unwinding secondary structures in 5’ UTR in ATP dependent manner.  It has an RNA binding domain.  It stimulates 4A’s helicase activity, but on its own it has no helicase activity.

eIF4-D (eIF5B)

112

Monomer, supposed to stimulate the whole complex of 80S formation?

eIF4-E(α)

25-26 kd

Monomer, this factor actually binds to 5’ end Cap structure.  Phosphorylation of this factor actually stimulates chain initiation; a rate-limiting step.  Stimulation of cell division with insulin or mitogen is due to 4E subunit’s phosphorylation.   It actually consists of 4-E-BP-1 and 4-E-BP-2

E4E-BP

4E binding protein

E-B respond to signals, when non p-lated binds to 4E and represses initiation, when 4EBP p-lated dissociates form 4E and activates initiation,

eIF4-F

complex

 It is cap binding complex, made up of 4-A (50kd), 4-E (24) and 4-G (220kd)

eIF- G

220kd 122  1  220kDa,

m7G,

Multimer, has multifarious functions, in capped mRNAs; it interacts with eIF4-E, eIF-3, eIF4-A, PABI and helps in recruiting 40s subunit.  In cap-less mRNA it interacts with eIF3, eIF4-A and another protein called X.  In capless and poly-A containing RNA, it interacts with PAB-I, eIF3 and eIF-4A.  It loads ribosomes onto mRNA.  Even cap containing mRNAs interacts with eIF4E, eIF3, eIF-4A and PAB-I and loads the ribosomes.  It has stabilizing effect on 4-E too.   It participates in all the initiating activities by serving as an adopter protein that can interact with a variety of proteins.  Translation of mRNA is greatly stimulated by the presence of poly-A tail binding PAB-1 and eIF-G.  They facilitate in recruiting ribosomes

Mnk1 and Mnk2

Called PHAS, Bp1 and BP2

4E kinases

eIF-5

45-48kd

It stimulates the association of 40s with 60s to form an initiation complex.  It facilitates the release of IF-3 and IF-2 from 40, which helps in 60 s joining the 40s. ribose dependent GTPase

eIF5B

112

Subunit joining

eIF-6

23-25kd

Binds to 60s and prevents 40 binding to 60s (an anti-dimerization factor)- like eIF3

PABp

72

Binds to poly-A tail, which in turn binds to eIFG

Factor

Mol.wt (KD)

Functions

eEF-1A- alpha(a

46-51

Equivalent to EF-Tu of bacteria, it is major factor, found abundantly; its activity is regulated, activated by GTP, then binds to a.a-tRNAs, no bias,

eEF1B,(b, g, d)

30,36,48

It is equivalent to EF-Ts of bacteria; factor is like GEF

eEF-2

92-93kd

It is like EF-G of bacteria-GTP binding factor, translocation factor,

Factor

Mol.wt (KD)

Functions

eRF1

48-50

Chain termination

eRF3

683aa (75kd)

Ribosome recycling factor

eEF-G

ATP bound

Assist eRF?

eRRF/ eABCE

Chain termination/RRF