Loss of Puma or both Bax plus Bak promotes clonogenic survival following IL-3 withdrawal. (A) Multiple independent, IL-3-dependent cell lines (n) were starved of IL-3 over a 5-day time course. Cell viability was determined by staining with FITC-conjugated annexin V and propidium iodide (PI) followed by flow cytometric analysis. Results show means ± SEM of 4 independent experiments. (B) Aliquots of the cell lines used in panel A were plated in soft agar with IL-3 after the indicated period of culture without IL-3. Colonies were counted after 21 days and the relative clonogenicity (see “Materials and methods”) determined. Data are the means ± SEM of 4 independent experiments.