EIF2AK4 and viral infectious disease: Upon diverse stimuli, mammalian eIF2alpha can be phosphorylated by four stress-responsive protein-serine/threonine kinases, namely PKR, that responds to virus infection; GCN2, that becomes activated in response to amino acids depletion, UV radiation, high salinity, and viral infection; HRI, that responds to oxidative agents, heat shock, and heme groups deficiency; and PERK, a transmembrane protein that becomes activated in response to perturbations in endoplasmic reticulum and unfolded proteins (18, 19).