Fig. 4. Cells with reduced expression levels of CK2α display decreased activity of E2F-1 transcription factor. (A) Cells were transfected with empty vector (EV) or a vector expressing firefly luciferase under the control of the E2F-1 promoter (E2F-1-Luc). Cells were synchronized by serum starvation essentially as described in Fig. 2A and, subsequently, harvested at the indicated time points. E2F-1 transcription activity was measured by a luciferase reporter assay employing 20 μg whole cell lysate. E2F-1 transcription activity is expressed in counts/s (cps). Mean values +/- SDEV, *P<0.005. (B, C) Expression of E2F and proteins indicated in (C) was analyzed by western blot employing whole lysate from synchronized cells as described in Fig. 2A. Experiments were performed three times obtaining similar results. One representative experiment is shown.