Serine/threonine-protein kinase which phosphorylates the alpha subunit of eukaryotic translation-initiation factor 2 (eIF2alpha), leading to its inactivation and thus to a rapid reduction of translational initiation and repression of global protein synthesis (By similarity). Involved in the unfolded protein response (UPR) triggered by several stresses including mitochondrial, osmotic and oxidative stresses, amino acid deprivation and UV irradiation, probably by phosphorylating and inhibiting eIF2alpha (PubMed:20733002, PubMed:23076791, PubMed:22719267, PubMed:23692540). In addition, leads to the selective translation/transcription of some mRNA including atf-5, pha-4 and gpdh-1 which are part of the UPR (PubMed:23076791, PubMed:23692540). Required for maintaining lifespan during amino acid starvation (PubMed:23692540). Involved in hypoxia-mediated adaptive protective response (PubMed:20733002). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] The protein kinase domain 1 is predicted to be catalytically inactive. RNAi-mediated knockdown results in slower development and shortened lifespan when exposed to mitochondrial stress. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. GCN2 subfamily.