EIF2AK3 and nutritional disorder: Indeed, the ISR integrates a range of cellular stresses which activate distinct eIF2α kinases; for example, amino acid deficiency activates GCN2 and ER stress kinase PERK (protein kinase R (PKR)‐like endoplasmic reticulum kinase), while viral or bacterial infection activates protein kinase R (PKR) and iron deficiency activates haem‐regulated kinase (HRI) by 23.