Four eIF2α kinases catalyze this phosphorylation in a cell type- and stress-specific manner: protein kinase RNA-activated (PKR) is activated by viral infection, PKR-like endoplasmic reticulum kinase (PERK) is activated by the accumulation of unfolded polypeptides in the lumen of the endoplasmic reticulum, general control non-derepressible 2 kinase (GCN2) is activated by amino acid starvation and ultraviolet (UV) light, and heme-regulated eIF2α kinase (HRI) is activated by heme deficiency and redox stress. This evidence concerns the gene EIF2AK2 and viral infectious disease.