Fig. 8. Binding of tubulin by Syt IX. GST, GST-Syt IX-C2A or GST-Syt IX-C2B (20 µg) immobilized on glutathione sepharose beads were incubated for 4 hours at 4°C with RBL cell extracts (500 µg) as described under Materials and Methods, in the absence or the presence of Ca²⁺ (3 mM) as indicated. Bound proteins were eluted by sample buffer, resolved on SDS-PAGE and analyzed by either Western blot, using anti-- or anti-ß-tubulin antibodies, or by staining the gel with Coomassie blue as indicated.