Eukaryotic initiation factors (eIFs) are proteins involved in the initiation phase of eukaryotic translation. These proteins help stabilize the formation of the functional ribosome around the start codon and also provide regulatory mechanisms in translation initiation. Eukaryotic initiation factor 2B (eIF2B) is a guanine nucleotide-exchange factor which mediates the exchange of GDP (bound to initiation factor eIF2) for GTP, thus regenerating the active [eIF2.GTP] complex that is required for peptide-chain initiation. The activity of eIF2B is a key control point for eukaryotic protein synthesis and is altered in response to viral infection, hormones, nutrients, growth factors and certain stresses. Eukaryotic translation initiation factor 4E (eIF4E) is best known for its function in the initiation of protein synthesis on capped mRNAs in the cytoplasm. Eukaryotic initiation factor (elF) 4A functions as a subunit of the initiation factor complex elF4F, which mediates the binding of mRNA to the ribosome.