Core component of multiple cullin-RING-based E3 ubiquitin-protein ligase complexes which mediate the ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:14578910, PubMed:16322693, PubMed:16678110, PubMed:18593899, PubMed:29779948, PubMed:30166453, PubMed:33854232, PubMed:33854239, PubMed:22118460). The functional specificity of the E3 ubiquitin-protein ligase complex depends on the variable substrate recognition subunit (PubMed:14578910, PubMed:16678110, PubMed:18593899, PubMed:29779948, PubMed:22118460). CUL4B may act within the complex as a scaffold protein, contributing to catalysis through positioning of the substrate and the ubiquitin-conjugating enzyme (PubMed:14578910, PubMed:16678110, PubMed:18593899, PubMed:22118460). Plays a role as part of the E3 ubiquitin-protein ligase complex in polyubiquitination of CDT1, histone H2A, histone H3 and histone H4 in response to radiation-induced DNA damage (PubMed:14578910, PubMed:16678110, PubMed:18593899). Targeted to UV damaged chromatin by DDB2 and may be important for DNA repair and DNA replication (PubMed:16678110). A number of DCX complexes (containing either TRPC4AP or DCAF12 as substrate-recognition component) are part of the DesCEND (destruction via C-end degrons) pathway, which recognizes a C-degron located at the extreme C terminus of target proteins, leading to their ubiquitination and degradation (PubMed:29779948). The DCX(AMBRA1) complex is a master regulator of the transition from G1 to S cell phase by mediating ubiquitination of phosphorylated cyclin-D (CCND1, CCND2 and CCND3) (PubMed:33854232, PubMed:33854239). The DCX(AMBRA1) complex also acts as a regulator of Cul5-RING (CRL5) E3 ubiquitin-protein ligase complexes by mediating ubiquitination and degradation of Elongin-C (ELOC) component of CRL5 complexes (PubMed:30166453). Required for ubiquitination of cyclin E (CCNE1 or CCNE2), and consequently, normal G1 cell cycle progression (PubMed:16322693, PubMed:19801544). Regulates the mammalian target-of-rapamycin (mTOR) pathway involved in control of cell growth, size and metabolism (PubMed:18235224). Specific CUL4B regulation of the mTORC1-mediated pathway is dependent upon 26S proteasome function and requires interaction between CUL4B and MLST8 (PubMed:18235224). With CUL4A, contributes to ribosome biogenesis (PubMed:26711351). Protein modification; protein ubiquitination. Component of multiple DCX (DDB1-CUL4-X-box) E3 ubiquitin-protein ligase complexes that seem to be formed of DDB1, CUL4A or CUL4B, RBX1 and a variable substrate recognition component which seems to belong to a protein family described as DCAF (Ddb1- and Cul4-associated factor) or CDW (CUL4-DDB1-associated WD40-repeat) proteins (PubMed:18593899, PubMed:10230407, PubMed:16678110, PubMed:17041588). Component of the DCX(DTL) complex with the putative substrate recognition component DTL (PubMed:17041588). Component of the DCX(DDB2) complex with the putative substrate recognition component DDB2 (PubMed:16678110). Component of DCX complexes part of the DesCEND (destruction via C-end degrons) pathway, which contain either TRPC4AP or DCAF12 as substrate-recognition component (PubMed:29779948). Component of the DCX(AMBRA1) complex with the substrate recognition component AMBRA1 (PubMed:30166453, PubMed:33854232, PubMed:33854239). Part of a complex with RBX1 and TIP120A/CAND1 (PubMed:12609982, PubMed:22118460). Interacts with RBX1, GRWD1, MLST8, SMU1, TLE2, TLE3, DCAF1, DDA1, DCAF6, DCAF17, DDB2, DCAF8, TIP120A/CAND1 and TMEM113 (PubMed:17041588, PubMed:16949367, PubMed:18235224). Interacts with cyclin E (CCNE1 or CCNE2) and with importins alpha-1 (KPNA2), alpha-3 (KPNA4), alpha-5 (KPNA1) and beta-1 (KPNB1) (PubMed:16322693, PubMed:19801544). May interact with WDR26, WDR51B, SNRNP40, WDR61, WDR76 and WDR5 (PubMed:17041588). Interacts (unneddylated form) with DCUN1D1, DCUN1D2, DCUN1D3, DCUN1D4 and DCUN1D5; these interactions promote the cullin neddylation (PubMed:23201271, PubMed:26906416). Neddylated. Deneddylated via its interaction with the COP9 signalosome (CSN) complex. The disease is caused by variants affecting the gene represented in this entry. Belongs to the cullin family.