Mediates down-regulation of protein synthesis in response to stress conditions by the phosphorylation of the alpha subunit of eIF-2 (tif211) on 'Ser-52'. Protein synthesis is inhibited at the level of initiation. Activity is inhibited in the presence of heme. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Autophosphorylated. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. GCN2 subfamily.