Figure 3.
Radiolabeled proteins in immunoprecipitated native CDK4 and CDK6 complexes from MRC-5 extracts under different growth states. Extracts from radiolabeled early passage MRC-5 fibroblasts logarithmically growing (lanes 1 and 2), arrested by growth in LS (lanes 3 and 4), 20 hr after gamma irradiation (Irrad) (lanes 5 and 6), and senescent MRC-5 cells (Sen) (lanes 7 and 8) or a SV40-transformed immortal human fibroblast line, GM639 (lanes 9 and 10) were immunoprecipitated under nondenaturing conditions with anti-CDK4 (A) or anti-CDK6 (B). Specificity of the precipitations was shown by competing the antibody with either a buffered saline solution (−) or peptides used to generate the antibodies in PBS (+). Extracts from the same number of cells were immunoprecipitated. Lanes 7–10 for both A and B were exposed three times longer to compensate for differences in radiolabel incorporation between extracts.