Practice question

JAK-STAT cascade involves Janus kinases JAK1-3, Tyk2 constitutively associated with cytokine receptors like interferon alpha, interleukin 6, growth hormone receptors lacking intrinsic kinase. Ligand binding dimerizes receptors activating JAKs autophosphorylating tyrosine residues creating SH2 docking sites for STAT proteins. STAT1-6 family contains SH2, DNA binding, transactivation domains. Upon phosphorylation at Tyr701, STAT dimerizes via reciprocal SH2-phosphotyrosine interactions, translocates to nucleus importin-mediated, binds GAS interferon gamma activated sequence motifs activating interferon response, proliferation, apoptosis genes. JAK is tyrosine kinase not transcription factor, FGF receptor RTK, MAP kinase serine-threonine, thus STAT provides direct transcription factor output.