Ba/F3 cells cultured in reduced IL-3 had a slowed G1 to S transition, but did not have reduced p53 induction or increased survival in response to VP-16. (A) Parental Ba/F3 cells were cultured in 1.0 ng/mL IL-3, which allows optimum growth, or in 0.1 ng/mL IL-3. After 48 hours, cell generation time was determined by enumerating the number of viable cells present in the cultures on subsequent days. To determine the ratio of the proportion of cells in G1 phase to the proportion of cells in S phase (G1/S), the cells were exposed to 30 μmol/L BrdU for 30 minutes, fixed, stained with anti–BrdU-FITC and PI, and subjected to FACScan analysis. The proportion of cells surviving exposure to 8 μg/mL VP-16 for 6 hours was determined as in Fig 3. (B) Ba/F3 cells cultured in 1.0 ng/mL or 0.1 ng/mL IL-3 for 48 hours were continued in cultured ± 8 μg/mL VP-16 for 150 minutes. Total cellular protein extracts were then obtained and subjected to Western blot analysis for p53.