The SCF (Skp1-Cullin 1-F-box) complex consists of four components: the invariable component Skp1 (adaptor protein), Rbx1 (RING finger protein) and Cullin1 (Scaffold protein), and the interchangeable F-box protein that functions as a receptor for target proteins. Skp2 recognizes the targeted substrates, which are presented closely to the E2 enzyme to ensure consequent conjugation of ubiquitin. The addition of polyubiquitin targets proteins to the 26S-proteasome for degradation. The specific substrates of Skp2 include p21, p27, p57, p103, Tob1, FOXO1, and c-Myc.