EIF-2

eIF-2 (Eukaryotic Initiation Factor 2) is a heterotrimer of subunits alpha, beta, and gamma. eIF-2 mediates the binding of methionyl-tRNAimet to the ribosome in a GTP-dependent manner.

eIF-2 is released from the ribosome bound to GDP as an inactive binary complex.

To participate in another round of translation initiation, this GDP must be exchanged for GTP.

Under steady-state conditions of translation, eIF-2 must be recycled in order to participate in another round of translation initiation.

eIF-2B
Conversion of the inactive eIF-2-GDP to the active eIF-2-GTP form is catalyzed by a guanine nucleotide exchange factor, eIF-2B.

Phosphorylation of the alpha subunit of eIF-2 inhibits translation initiation by impairing the eIF-2B-catalyzed guanine nucleotide exchange reaction.