Structure of Janus kinases (Jaks), signal transducers andactivators 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. Theamino-terminus of the Jaks appears to be important for association withcytokine 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 thatis 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 othertranscription factors. SOCS proteins share a similar strucuture with a centralSH2 domain, a region at the amino-terminus that is variable in both length andin amino acid sequence, and a region of homology at the carboxy-terminus termedthe 'SOCS box'.