Figure 4.

Schematic representation of the interplay between the ubiquitinating activities of APC/C and SCF complexes during cell cycle. (i) During G₁ phase, APC/C^CDH1 targets several F-box substrate receptors of SCF complexes, including SKP2 and TOME-1, and the SKP2 cofactor CKS1. In addition, CDC20 is also targeted to ubiquitination and degradation by APC/C^CDH1. While CDH1 is subject to self-ubiquitination during G₀ and G₁ phases within the context of the APC/C complex (ii), the degradation of the free released phosphorylated form is mediated by an SCF complex during S phase (iii). (iv) During S and G₂ phases, APC/C^CDC20 is inhibited by the F-box protein EMI1 (iv-a); however, in the M phase, EMI1 is targeted for destruction by SCF^β-TRCP alleviating the inhibition of APC/C^CDC20 (iv-b). (v) CDC20 is targeted in a self-catalytic manner during the spindle-associated checkpoint