FIG. 3.

Amounts and associated activities of cyclins D1 and D3 in p27/p21^−/− MEFs infected with Ad-p27^Kip1. Asynchronously growing p21/p27^−/− MEFs were infected with Ad-p27^Kip1 at the indicated MOIs. Cells were harvested 25 h after infection. Amounts of p27^Kip1, cyclin D1, cyclin D3, and cdk4 were determined by Western blotting of cell extracts. Amounts of cyclin D1-associated cdk4, cdk4-associated cyclin D3, and cdk4-associated p27^Kip1 were determined by immunoprecipitation (IP) and immunoblot analysis. Kinase activity was assayed in cyclin D1 and cdk4 immunoprecipitates with GST-Rb as substrate. pRb, phosphorylated Rb.