Cullins are modified by NEDD8 in vitro and the hCUL-2 modification is stimulated by wild-type pVHL. (A) hCUL-1 and hCUL-2 cDNAs (1 μg each) were translated in a reticulocyte lysate system simultaneously with a pVHL cDNA (1 μg) in the presence of recombinant GST or GST–NEDD8 protein (1 μg). Reaction mixtures were processed by SDS/PAGE and autoradiography. (B) hCUL-2 cDNA was translated in a reticulocyte lysate system simultaneously with increasing amounts of pVHL or pVHLΔ157 cDNAs (0.1, 0.5, 1, 2 μg), and reaction mixtures were processed as in A. (C) The NEDD8 conjugated hCUL-2 bands were quantified by densitometry of different exposures of autoradiographs. The values were plotted as fold induction vs. the value obtained without addition of pVHL (filled bars, wild-type pVHL; open bars, pVHLΔ157).