See also Protein Kinases Generally
Introduction:
The JAK-STAT family of proteins for signal transduction consists of 4 Janus family tyrosine kinases (JAKI-1, JAK-2, JAK-3, and TYK-2) and seven latent cytosolic transcription factors.
The Janus kinase (JAK) family of proteins consists of 4 tyrosine kinases, JAK1, JAK2, JAK3 and Tyk2, which are central to the intracellular signaling of type I and type II cytokine receptors. The term JAK refers to either JAK1, JAK2, JAK3 or Tyk2, or any combination thereof. Each JAK selectively associates with receptor subunits which dimerize (or multimerize) to form functional receptors.
Activated JAKs phosphorylate specific tyrosines in the receptor subunits of the complex and members of a family of transcription factors called bind to these phosphorylated tyrosine residues. The binding of STATs to receptor subunits is mediated by the joining of the SH2 domain on the STAT with the docking site created by the JAK mediated phosphorylation of a particular tyrosine on receptor subunits. STATs now can translocate from the receptor docking sites at the membrane to the nucleus where they initiate the transcription of specific genes. A particular STAT will only recognize certain sequence motifs and thus can interact only with the promoters of certain genes.