JAKs bind to the box1 motif (residues 297-305) of the Growth Hormone Receptor (GHR) (Argetsinger et al. 1993), a proline-rich region just inside the cell membrane. Binding is mediated largely by the JAK N-terminal FERM domain (Frank et al. 1995, He et al. 2003). JAK 2 binding enhances the stability of GHR (He et al. 2005).