EIF2AK3 and infection: Mammalian cells possess four different eIF2α kinases (GCN4, PERK, PKR, and HRI) that are activated by distinct stress conditions including nutritional deprivation (GCN4), endoplasmic reticulum stress (PERK), infection by viral-derived RNA (PKR) and heat/oxidative/heme-induced stresses (HRI).