| Background |
Members of the Janus family of tyrosine kinases (Jak1, Jak2, Jak3, and Tyk2) are activated by ligands binding to a number of associated cytokine receptors Upon cytokine receptor activation, Jak proteins become autophosphorylated and phosphorylate their associated receptors to provide multiple binding sites for signaling proteins. These associated signaling proteins, such as Stats Shc insulin receptor substrates and focal adhesion kinase (FAK) typically contain SH2 or other phospho-tyrosine-binding domains.The tyrosine residues 1022/1023 of Jak1 in the putative activation loop are the homologous tyrosine residues 1054/1055 in Tyk2, which are important in the regulation of Tyk2 kinase activity.
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