Cullin (Cullin-1, CUL1) is a core component of multiple cullin-RING-based SCF (SKP1-CUL1-F-bo, Xenopus/Amphibian, protein) E3 ubiquitin-protein ligase comple, Xenopus/Amphibian,es, which mediate the ubiquitination of proteins involved in cell cycle progression, signal transduction and transcription. In the SCF comple, Xenopus/Amphibian,, cullin serves as a rigid scaffold that organizes the SKP1-F-bo, Xenopus/Amphibian, protein and RB, Xenopus/Amphibian,1 subunits. Cullin contributes to catalysis through positioning of the substrate and the ubiquitin-conjugating enzyme.