Fig. 3. Analysis of binding domains between SgIII and CPE. To investigate the specific binding domains of SgIII (A) and CPE (B), four GST-SgIII fusion proteins, full-length SgIII 23-471, SgIII 23-186, SgIII 187-373 and SgIII 374-471, were tested for binding to CPE; and five GST-CPE fusion proteins, pro-form CPE 23-477, mature form CPE 43-477, CPE 131-365, CPE 23-281 and CPE 332-477, were tested for binding to SgIII. GST-fusion proteins immobilized on glutathione beads were incubated with AtT-20 cell extract at pH 5.5 with 10 mM Ca²⁺. The precipitates were detected by antibody to CPE (upper panel) or antibody to SgIII (lower panel) antibody. Asterisks indicate the pro-form of SgIII. One-twentieth of the cell extract was run on lane 6 (A) and lane 7 (B) n=4 (A) and n=3 (B).