HFFs with stable expression of empty vector (C) or HPV16 E7 (E7) were transfected with non-targeting control siRNAs, siMad2, or siBubR1 before subjected to a double thymidine block. Western blot analyses of pRB, Mad2, BubR1, pH3S10, histone H3, cyclin B, cyclin A and actin are shown. Cyclin B and cyclin A quantifications relative to actin are indicated above the respective blots. Values are presented relative to the highest (1) in each condition. Shown here is a representative experiment; similar results were obtained in three additional experiments.