FIG. 6.

Deletion of RGS, GID, or DIX domains. (A) Myc epitope-tagged ΔRGS (deletion of aa 80 to 290), ΔGID (deletion of aa 324 to 504), and ΔDIX (deletion of aa 778 to 842) proteins were expressed in oocytes along with Xenopus GSK-3β. Interaction with GSK-3β was assessed by immunoprecipitation with the Myc antibody followed by immunoblotting with anti-GSK-3β (as in Fig. 1C); GSK-3β activity was assayed by tau phosphorylation (as in Fig. 1B). Data for FL Xaxin and GID-2 are from Fig. 1 and 3, respectively. (B) ΔRGS inhibits GSK-3β-mediated tau phosphorylation in a dose-rependent manner. GSK-3β phosphorylates tau, as assessed by a decrease in electrophoretic mobility (lane 2, 20 ng of RNA; lane 3, 2 ng; lane 4, 1 ng; lane 5, 0.4 ng), and this is inhibited by coexpression of ΔRGS (20 ng; lanes 6 to 9). ΔRGS also inhibits GSK-3β (2 ng) in a dose-dependent manner (lane 10, 20 ng of ΔRGS mRNA; lane 11, 2 ng; lane 12, 1 ng; lane 13, 0.4 ng). Note that the highest level of GSK-3β expression overcomes the inhibition by ΔRGS (lane 6).