Non-receptor kinase involved in various processes including cell growth, development, cell migration, innate and adaptive immunity (PubMed:10995743, PubMed:10542297). Plays both structural and catalytic roles in numerous cytokines and interferons signaling (PubMed:10542297). Associates with cytokine and growth factor receptors and activate STAT family members including STAT1, STAT3, STAT4 or STAT6 (PubMed:10542297, PubMed:7638186). The heterodimeric cytokine receptor complexes are composed of a TYK2-associated receptor chain (IFNAR1, IL12RB1, IL10RB or IL13RA1) which serves as the signal transducing chain harboring STAT docking sites once phosphorylated by TYK2, and a second receptor chain associated either with JAK1 or JAK2 (PubMed:10542297, PubMed:7526154, PubMed:25762719). In turn, recruited STATs are phosphorylated, form homo- and heterodimers, translocate to the nucleus, and regulate cytokine/growth factor responsive genes. Negatively regulates STAT3 activity by promototing phosphorylation at a specific tyrosine that differs from the site used for signaling (PubMed:29162862). ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] The protein kinase 1 domain (also termed pseudokinase domain) mediates autoinhibition of the TYK2 kinase domain. Interacts with JAKMIP1 (PubMed:15277531, PubMed:20478313). Interacts with PIK3R1; this interaction is important for cell migration (PubMed:10995743). (Microbial infection) Interacts with Epstein-Barr virus protein LMP1; this interaction inhibits TYK2-mediated interferon signaling. (Microbial infection) Interacts with papillomavirus-18 protein E6; this interaction impairs JAK-STAT activation by interferon-alpha. Observed in all cell lines analyzed. Expressed in a variety of lymphoid and non-lymphoid cell lines. The FERM domain mediates interaction with JAKMIP1. Phosphorylated (PubMed:7638186). Phosphorylations at Tyr-1054 and Tyr-1055 induce kinase activation (PubMed:8702790). The disease is caused by variants affecting the gene represented in this entry. Belongs to the protein kinase superfamily. Tyr protein kinase family. JAK subfamily. TYK2 mutation db