For example, the PKR kinase is activated by double-stranded RNA (as occurs in viral infection), the PERK kinase is activated as part of the endoplasmic reticulum stress/unfolded protein response pathways, the GCN2 kinase is activated in response to amino acid depletion and the Heme Regulated Inhibitor kinase HRI (EIF2AK1) is activated by heme deficiency [19]. Here, EIF2AK2 is linked to viral infectious disease.