EIF2AK4 and viral infectious disease: Phosphorylation of eIF2α results from activation of one or more stress-sensing serine/threonine kinases [20], including GCN2 (activated by amino acid deprivation [21]), HRI (monitors oxidative stress/ROS levels [22]), PERK (senses endoplasmic reticulum (ER) stress [23, 24]) and PKR (activated by double-stranded RNA during viral infections, UV exposure and heat shock [25]).