EIF2AK4 and viral infectious disease: Current studies found that eIF2α kinase contains four distinct serine‐threonine kinase families, which are PERK (EIF2AK3), PKR (EIF2AK2), general control non‐derepressible‐2 (GCN2, EIF2AK4) and haem‐regulated inhibitor (HRI, EIF2AK1), they respectively sense a variety of different cell stress responses, including viral infections, protein toxicity and low levels of essential nutrients (such as amino acids and haem).57