IFN-induced dsRNA-dependent serine/threonine-protein kinase that phosphorylates the alpha subunit of eukaryotic translation initiation factor 2 (EIF2S1/eIF-2-alpha) and plays a key role in the innate immune response to viral infection (By similarity). Inhibits viral replication via the integrated stress response (ISR): EIF2S1/eIF-2-alpha phosphorylation in response to viral infection converts EIF2S1/eIF-2-alpha in a global protein synthesis inhibitor, resulting to a shutdown of cellular and viral protein synthesis, while concomitantly initiating the preferential translation of ISR-specific mRNAs, such as the transcriptional activator ATF4 (By similarity). Exerts its antiviral activity on a wide range of DNA and RNA viruses (By similarity). Also involved in the regulation of signal transduction, apoptosis, cell proliferation and differentiation: phosphorylates other substrates including p53/TP53, PPP2R5A, DHX9, ILF3 and IRS1 (By similarity). In addition to serine/threonine-protein kinase activity, also has tyrosine-protein kinase activity and phosphorylates CDK1 at 'Tyr-4' upon DNA damage, facilitating its ubiquitination and proteosomal degradation (By similarity). Either as an adapter protein and/or via its kinase activity, can regulate various signaling pathways (p38 MAP kinase, NF-kappa-B and insulin signaling pathways) and transcription factors (JUN, STAT1, STAT3, IRF1, ATF3) involved in the expression of genes encoding pro-inflammatory cytokines and IFNs (By similarity). Activates the NF-kappa-B pathway via interaction with IKBKB and TRAF family of proteins and activates the p38 MAP kinase pathway via interaction with MAP2K6 (By similarity). Can act as both a positive and negative regulator of the insulin signaling pathway (ISP) (By similarity). Negatively regulates ISP by inducing the inhibitory phosphorylation of insulin receptor substrate 1 (IRS1) at 'Ser-312' and positively regulates ISP via phosphorylation of PPP2R5A which activates FOXO1, which in turn up-regulates the expression of insulin receptor substrate 2 (IRS2) (By similarity). Can regulate NLRP3 inflammasome assembly and the activation of NLRP3, NLRP1, AIM2 and NLRC4 inflammasomes (By similarity). Plays a role in the regulation of the cytoskeleton by binding to gelsolin (GSN), sequestering the protein in an inactive conformation away from actin (By similarity). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Initially produced in an inactive form and is activated by binding to viral dsRNA, which causes dimerization and autophosphorylation in the activation loop and stimulation of function. ISGylation can activate it in the absence of viral infection. Can also be activated by heparin, pro-inflammatory stimuli, growth factors, cytokines, oxidative stress and the cellular protein PRKRA. Activity is markedly stimulated by manganese ions. Activation is blocked by the cellular proteins TARBP2, DUS2L, NPM1, NCK1 and ADAR (By similarity). Homodimer (By similarity). Interacts with DNAJC3 (By similarity). Interacts with STRBP. Forms a complex with FANCA, FANCC, FANCG and HSP70 (By similarity). Interacts with ADAR/ADAR1 (By similarity). The inactive form interacts with NCK1 and GSN. Interacts (via the kinase catalytic domain) with STAT3 (via SH2 domain), TRAF2 (C-terminus), TRAF5 (C-terminus) and TRAF6 (C-terminus). Interacts with MAP2K6, IKBKB/IKKB, IRS1, NPM1, TARBP2, NLRP1, NLRP3, NLRC4 and AIM2. Interacts (via DRBM 1 domain) with DUS2L (via DRBM domain). Interacts with DHX9 (via N-terminus) and this interaction is dependent upon activation of the kinase (By similarity). Autophosphorylated on several Ser, Thr and Tyr residues. Autophosphorylation of Thr-411 is dependent on Thr-406 and is stimulated by dsRNA binding and dimerization. Autophosphorylation apparently leads to the activation of the kinase. Tyrosine autophosphorylation is essential for efficient dsRNA-binding, dimerization, and kinase activation (By similarity). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. GCN2 subfamily.