Cullin-4B (CUL4B) is a core component of multiple cullin-RING-based E3 ubiquitin-protein ligase complexes which mediate the ubiquitination and subsequent proteasomal degradation of target proteins. CUL4B may act within the complex as a scaffold protein, contributing to catalysis through positioning of the substrate and the ubiquitin-conjugating enzyme [, ]. Mutations in the CUL4B gene cause X-linked mental retardation [].Cullins are a family of hydrophobic proteins that act as scaffolds for ubiquitin ligases (E3). Cullins are found throughout eukaryotes. Humans express seven cullins (Cul1, 2, 3, 4A, 4B, 5 and 7), each forming part of a multi-subunit ubiquitin complex.
