Fig. 7. IE2-arrested cells resemble cells at G₁–S transition in their state of cyclin–cdk activity. U373 cells were transfected with the empty expression plasmid pSG5-3HA and pSG5CD20. After removal of the DNA precipitates, cells were treated for 32 h with aphidicolin (Aph) or hydroxyurea (HU) or left untreated (–). After harvesting, cells were sorted as detailed in Figure 2. (A) Cell cycle distributions of CD20-positive, PI-stained cells were analysed by flow cytometry. (B) Kinase activities associated with cyclins E, A and B in extracts of CD20-positive cells were assayed as detailed in the legend to Figure 4B.