FIG. 1.
Presence of the R24C mutation in Cdk4 results in a deregulated Cdk4R24C kinase. (a) Immune-complex kinase assays using anti-Cdk4 specific antibodies without (lanes 1 to 3) or with (lanes 4 to 6) the presence of a competing Cdk4 peptide and pRb substrate were performed with 500 μg of protein extracts isolated from Cdk4+/+, Cdk4+/R24C, and Cdk4R24C/R24C MEF cultures. The presence of the phosphorylated GST-pRb substrate is indicated. (b) Increased Cdk4R24C kinase activity results hyperphosphorylation of Rb family proteins pRb (top), p107 (middle), and p130 (bottom). Arrows indicate the phosphorylated forms of the proteins.