FIG. 4.

Ras transforms MEFs lacking p53^−/−. (A to D) p53^−/−, Cdk2^−/− p53^−/−, Cdk4^−/− p53^−/−, and Cdk2^−/− Cdk4^−/− p53^−/− MEFs were infected with empty vector (left) or activated Ras^G12V (right). Colonies were stained with Giemsa after 10 days of culture. The numbers of colonies are the averages from three 10-cm plates.