EIF2AK2 and viral infectious disease: Four eIF2 kinases have been identified to be responsible for eIF2α phosphorylation, such as protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK, responsible for endoplasmic reticulum stress), general control nonderepressible 2 (GCN2, activated by amino acid starvation), protein kinase R (PKR, up-regulated by viral infections), and heme-regulated eIF2α kinase (HRI, induced by oxidative stress or heme deprivation) [26,27,28,29].