EIF2AK4 and viral infectious disease: In cells exposed to diverse stress conditions such as heme deprivation, viral infection, endoplasmic reticulum (ER) stress, and amino acid starvation, four mammalian protein kinases—HRI/EIF2AK1 (eIF2α kinase 1), PKR/ EIF2AK2 (eIF2α kinase 2), PERK/EIF2AK3 (eIF2α kinase 3), and GCN2/EIF2AK4 (eIF2α kinase 4)—phosphorylate serine 51 of the α subunit of the eIF2 complex (Donnelly et al., 2013; Wek et al., 2006) (Fig. 1).