Stat5 tyrosine phosphorylation was seen in response to GH in CHO cells expressing mouse GHR forms capable of binding JAK2 (Smit et al. 1996). Similar results were obtained using the porcine receptor (Wang et al. 1996). Thus Jak2 phosphorylates Stat5, the phosphorylated monomers form dimers and translocate to the nucleus (Darnell et al. 1994).