 Structural determinants that regulate the interactions between Jak3 and cytoskeletal proteins of the villin / gelsolin family have also been characterized.Functional reconstitution of kinase activity by recombinant Jak3 using Jak3-wt or villin/gelsolin-wt as substrate showed that Jak3 autophosphorylation was the rate-limiting step during interactions between Jak3 and cytoskeletal proteins.Kinetic parameters showed that phosphorylated (P) Jak3 binds to P-villin with a dissociation constant (Kd) of 23 nM and a Hill's coefficient of 3.7.