Fig. 1.

Schematic illustration of an SCF-type of E3 ubiquitin ligase complex. The SCF (Skp1-Cullin1-F-box) complex consists of 4 components: Skp1, Rbx1, Cullin1, and the F-box protein that is responsible for substrate recognition. β-TrCP (β-transducin repeats-containing protein) recognizes the targeted proteins, which are presented close to the E2 enzyme to ensure consequent conjugation of ubiquitin to the targeted substrates. Polyubiquitylated substrates are subsequently targeted for degradation by the 26S proteasome. Known β-TrCP substrates include EMI-1, Wee1, Cdc25A, caspase-3, PDCD4, Snail, IκB, ATF4, p100, p105, Mdm2, and many others. See text for definitions.