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. 2011 Sep 22;44(5):391–400. doi: 10.1111/j.1365-2184.2011.00767.x

Figure 4.

Figure 4

  Model of spindle assembly checkpoint signalling. (a) Unattached kinetochore (K) serves as a platform for SAC proteins BubR1, Bub3, and Mad2 to generate the mitotic checkpoint complex (50) that binds to Cdc20 preventing it from activating APC/C, the E3 ubiquitin ligase that targets Securin and Cyclin B for degradation by the 26S proteasome, thereby inhibiting anaphase onset. (b) According to the Mad2 template model, a constitutively closed conformation of Mad2 (C‐M2) bound to Mad1 serves as receptor at unattached kinetochore for cytosolic open form of Mad2 (O‐M2) to switch this latter to C‐Mad2 bound to Cdc20. C‐Mad2/Cdc20 complex acts as a structural equivalent of Mad1/Mad2 to convert more O‐Mad2 into Cdc20 bound C‐Mad2 in the cytosol, leading to signal amplification (93, 94).