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