Figure 1.

Structure of Janus kinases (Jaks), signal transducers and activators of transcription (Stats), and suppressors of cytokine signaling (SOCS). Regions of homology shared by Jaks have been termed Jak homology (JH) domains. JH1 is a kinase domain and JH2 is a pseudo-kinase domain. The amino-terminus of the Jaks appears to be important for association with cytokine receptors subunits. Stats have a conserved tyrosine residue, phosphorylation of which allows Stat dimerization; a src homology (SH2) domain that mediates the dimerization; and an amino-terminal region that is known to play a role in the dimerization of Stats dimer. The amino-terminal, carboxy-terminal and coiled-coil regions of Stats can interact with other transcription factors. SOCS proteins share a similar strucuture with a central SH2 domain, a region at the amino-terminus that is variable in both length and in amino acid sequence, and a region of homology at the carboxy-terminus termed the 'SOCS box'.