Stimulation of the CRL4CRBN-mediated-ubiquitination of CK1α by Nedd8.A, time course of CK1α ubiquitination by CRL4CRBN and Nedd8–CRL4CRBN. B, time course of CK1α ubiquitination by Nedd8–CRL4CRBN with E2–Ub (UbcH5c–Ub and Cdc34b–Ub) treated with or without apyrase. Reactions were carried out as described in the Experimental procedures section. Both high-and low-contrast fluorescent scans are shown. Percentage of CK1α consumed is indicated. CK1α, casein kinase 1α; CRBN, cereblon; CRL, Cullin–RING E3 Ub ligase; Nedd8, neural precursor cell expressed, developmentally downregulated 8.