(F) GSK3-mediated phosphorylation of threonine 236 promoted SOX9 interaction with recombinant SCF-FBW7α in vitro. Bead-immobilized IVT HA-SOX9 were either untreated or phosphorylated with GSK3 as described in (E) prior to further incubation with recombinant SCF-FBW7α for in vitro binding assay. Immunoblot showed FBW7α protein in the in vitro binding reaction (input) as well as those which had been eluted from the untreated and GSK3-treated immobilized SOX9. The set of blots shown is representative from 3 independent experiments. 