STAT and JAK structure. The STATs share several conserved domains, including an amino-terminal domain (NH₂), a coiled-coil domain, the DNA-binding domain, a linker domain, an SH2 domain, and a tyrosine activation domain (P). The carboxy-terminal transcriptional activation domain is conserved in function, but not in sequence. Likewise, the JAKs share seven regions of high homology, JH1–JH7. JH1 has been shown to encode the kinase. JH2 represents a pseudokinase domain, which appears to regulate JH1 catalytic activity. JH3–JH7 have been implicated in receptor association. See text for details.