Figure 2.

Model for cytokine signal transduction. Cytokines associate with cytokine receptor subunits and activate janus kinases (Jaks). The Jaks in turn phosphorylate tyrosine-based docking sites on the receptor. signal transducers and activators of transcription (Stats) then bind via their src homology (SH)2 domains. The STATs are then phosphorylated by the JAKs, form homo-hetero-dimers and then translocate into the nucleus, where they bind target sequences like γ activated sequence (GAS) motif. Transcriptional activation of genes typically requires the coordinated function of multiple accessory transcription factors. Additionally, serine phosphorylation of some Stats may be important for maximal transcription of target genes.