Fig. 4. Kinase activities of cyclin E, A and B complexes in IE2-expressing cells. U373 cells were transfected and sorted as described in Figure 2. (A) Equal amounts of whole-cell extracts from CD20-positive cells were separated by SDS–PAGE and analysed by immunoblotting with antibodies against cyclins E, A and B. A vigilin-specific antibody was used to control for equal protein loading. A non-specific background band is marked by a star. (B) The same extracts were used for immunoprecipitations (IP) with antibodies against the indicated cyclins followed by kinase assays using histone H1 (H1) as substrate.