Overproduction of polypeptides corresponding to the amino terminus of the F-box proteins Cdc4p and Met30p inhibits ubiquitin ligase activities of their SCF complexes.

Ubiquitin ligases direct the transfer of ubiquitin onto substrate proteins and thus target the substrate for proteasome-dependent degradation. SCF complexes are a family of ubiquitin ligases composed of a common core of components and a variable component called an F-box protein that defines substrate specificity. Distinct SCF complexes, defined by a particular F-box protein, target different substrate proteins for degradation.