EIF2AK3 and viral infectious disease: In addition to GCN2, there are three other mammalian eIF2α kinases: PERK (EIF2AK3/PEK), PKR (EIF2AK2) and HRI (EIF2AK1), which are activated by endoplasmic reticulum (ER) stress, viral infection, and heme deprivation in reticulocyte cells, respectively [6].