The pocket domain of the RB1 tumor suppressor protein binds to the N-terminal domain of SKP2, a component of the SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complex, whose targets include the cyclin-dependent kinase (CDK) inhibitor p27Kip1 (CDKN1B) (Ji et al. 2004, Binne et al. 2007). RB1 is able to simultanously interact with SKP2 and with FZR1 (Cdh1). FZR1 is a substrate-specific adapter for the anaphase promoting complex/cyclosome (APC/C). The interaction with FZR1 involves a different subregion of the pocket domain than the interaction with SKP2, and is partially dependent on the LxCxE binding cleft (Binne et al. 2007).