 Phosphorylation takes place at the α-subunit, which is a target for a number of serine kinases that phosphorylate serine 51.Those kinases act as a result of stress such as amino acid deprivation (GCN2), ER stress (PERK), the presence of dsRNA (PKR) heme deficiency (HRI), or interferon.Once phosphorylated, eIF2 shows increased affinity for its Guanine nucleotide exchange factor eIF2B.