down regulation on cell cycle distribution. MDA-MB-231 cells were treated for 72 h with three separate siRNAs targeting CDC23. Thereafter the cell cycle distribution was analyzed with flow cytometry (A) and CDC23 protein levels were analyzed with Western blot (B). The data in A are mean ± SEM from three separate experiments. Asterisks indicate statistically significant differences (* p < 0.05, *** p < 0.001, paired t-test) compared to control cells.