The APC core contains multiple subcomplexes. The budding yeast APC core is an approximately 1 MDa complex of 13 subunits (Table 1), including the nine key subunits shown here. One subcomplex (dark green) contains the cullin subunit Apc2 and the RING-domain protein Apc11, which recruits E2s. Another subcomplex (light green) contains the three TPR-containing subunits, Cdc27, Cdc23 and Cdc16, as well as two subunits, Apc4 and Apc5, that help connect them to the rest of the APC via Apc1. The TPR-containing subunits provide binding sites for the activator (Cdh1 or Cdc20), which contains at least two APC-interaction motifs, the Ile-Arg (IR) motif and the C-box, as well as a large WD40 repeat sequence that is likely to form a propeller-like binding site for substrate.