 Functional characterization showed that Jak3 autophosphorylation was the rate-limiting step during Jak3 trans-phosphorylation of β-catenin, where Jak3 directly phosphorylated three tyrosine residues, viz.Tyr30, Tyr64, and Tyr86 in the N-terminal domain (NTD) of β-catenin.However, prior phosphorylation of β-catenin at Tyr654 was essential for further phosphorylation of β-catenin by Jak3.