Figure 4.

Growth enhancement of c-Myc-deficient cells by ectopic CDK4 expression. (A) Western blot analysis of CDK4 expression in c-Myc-deficient RAT1 cell infected with a CDK4-encoding retrovirus and a gene conferring hygromycin resistance. CDK4-P1, -P2, and -P3 represent pools of hygromycin-resistant c-Myc −/− cells. CDK4, endogenous CDK4. (B) The pools from A were analyzed for growth rates. Cells were seeded in DMEM containing 10% calf serum and counted at 24-h intervals. Each time point represents the average of two independent experiments. β-Gal, β-galactosidase.