EIF2AK4 and viral infectious disease: In mammalian ISR, four eIF2α kinases, (heme regulated inhibitor of translation (HRI), dsRNA-activated protein kinase (PKR), PKR-like endoplasmic reticulum kinase (PERK) and general control nonderepressible-2 (GCN2)) catalyze phosphorylation of eukaryotic initiation factor 2α (eIF2α) at serine51 residue in response to different stress signals; heme deficiency (HRI), viral infection (PKR), ER stress (PERK), and amino acid deficiency (GCN2) [18].