Figure 7.

Model of O-Mad2:C-Mad2 interaction. (A) A cartoon summarizing the possible role of Mad1-bound C-Mad2 in the conversion of O-Mad2 into Cdc20-bound C-Mad2. Only the critical secondary structure elements are displayed. Panel 1 shows that the α3-helix of O-Mad2 docks on the α3-helix and β8 strand of C-Mad2. While the α3-helix remains docked onto C-Mad2, a displacement of the O-Mad2 core allows the passage of β1. The displacement is made possible by the long and flexible α3–β5 loop. After displacing β1, the C-terminal tail can move into its final position upon capturing Cdc20. (B) Mad2^ΔN15, Mad2^ΔC and Mad2^ΔN15 were tested for association with C-Mad2^wt prebound to GST-Cdc20^111−138. Mad2^ΔC binds readily to C-Mad2, while Mad2^ΔN15 is a slow binder. The experiment was repeated at least three times with basically identical results.