Figure 1.

Rb^−/− MEFs are defective in cell cycle arrest after γ-irradiation. (A) Asynchronous cultures of Rb^−/− and wild-type littermate control MEFs were γ-irradiated at the indicated doses. Twenty-four hours after treatment, cells were labeled with BrdUrd for 8 hr. BrdUrd incorporation was then assessed by immunocytochemistry. Data from three independent samples are presented as the percentage of cells that incorporated BrdUrd in irradiated vs. unirradiated cultures. (B) Rb^−/− and wild-type MEFs infected with pBabe or pBabe pRB retroviruses were treated as in A. (C) Expression of pRB in infected cells from B was confirmed by Western blotting.