The initiation of protein synthesis in eukaryotic cells is regulated by interactions
between protein initiation factors and RNA molecules. The eukaryotic
initiation complex is composed of three subunits, designated eIF2α, eIF2β
and eIF2γ (eukaryotic translation initiation factor 2 α, β and γ, respectively),
all of which work in concert to form a ternary complex with GTP and tRNA in
the early stages of protein synthesis. eIF2α, also known as EIF2S1 or EIF2, is
a 315 amino acid subunit of the eukaryotic initiation complex that functions
to bind tRNA to the 40S ribosomal subunit (in a GTP-dependent manner),
thereby initiating translation. In addition, the phosphorylation state of eIF2α
controls the rate of tRNA translation. When eIF2α is not phosphorylated,
translation occurs at a normal rate. However, upon phosphorylation by one of
several kinases, eIF2α is stabilized, thus preventing the GDP/GTP exchange
reaction and slowing translation.