Non-receptor kinase involved in various processes including cell growth, development, cell migration, innate and adaptive immunity (PubMed:11070174). Plays both structural and catalytic roles in numerous cytokines and interferons signaling. Associates with cytokine and growth factor receptors and activate STAT family members including STAT1, STAT3, STAT4 or STAT6 (PubMed:22859374). 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. 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 (By similarity). 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. Interacts with PIK3R1; this interaction is important for cell migration. The FERM domain mediates interaction with JAKMIP1. Deficient mice are viable and fertile but display multiple immunological defects, most prominently high sensitivity to infections and defective tumor surveillance. Absence of TYK2 results in increased resistance against allergic, autoimmune and inflammatory disease. Belongs to the protein kinase superfamily. Tyr protein kinase family. JAK subfamily. Truncated N-terminus. Truncated N-terminus.