Figure 3. Overexpression of cyclin E1, but not cyclin E2, alters APC activity. HU-synchronized cells were released into the cell cycle for 0, 9, 24 and 30 h. Data are representative of, or pooled from, quadruplicate experiments. Error bars where shown represent S.E.M. (A) Cell lysates were immunoblotted for cyclins E1 and E2, Cdh1, securin, Cdc20 and β-actin. (B) Densitometry was performed on Cdh1 immunoblots and normalized to β-actin. (C) G₂/M phase expression of cyclin B1, securin, and Cdc20 were quantitated relative to levels at 9 h. Band intensities were normalized to β-actin. (D) Lysates collected 12 h post-HU release were immunoprecipitated with antibodies to cyclins E1 and E2 and IgG control, and then immunoblotted for Cdh1, cyclin E1, cyclin E2, and CDK2. IP, immunoprecipitate; IB, immunoblot; IgG, immunoglobulin G. Arrow(s) indicate protein(s) of interest.