EIF2AK2 and viral infectious disease: Importantly, in addition to PERK, the other three kinases catalyze eIF2α phosphorylation, without the concomitant activation of the IRE1 and ATF6 pathways: protein kinase R (PKR), in response to viral infection; general control nonderepressible 2 kinase (GCN2), in response to amino acid starvation; and heme-regulated inhibitor kinase (HRI), in response to heme deficiency.