Fig. 2. Failure to replicate following prolonged exposure to hydroxyurea or aphidicolin is not dependent on p53 or pRB function. T-antigen-transformed REF-52 cells (TAG) were subjected to analysis as for REF-52 (Fig. 1). FACScan analysis of random cycling TAG cells treated with aphidicolin (10 µM) or hydroxyurea (2 mM) for the indicated times, then released for 24 hours into nocodazole (0.25 µg/ml), shows failure to progress in the cell cycle after 30 hours of treatment.