FIG. 4.

MEFs exhibit a biphasic response to E2F3 stimulation. (A) E2F3 induction enhances S-phase entry in cycling MEFs. The percentage of MEFs incorporating bromodeoxyuridine upon E2F3 induction is shown. NI, not infected; ER-E2F3, infected cells not induced;ER-E2F3 + OHT, infected cells induced with 4-hydroxy tamoxifen. (B) Transient induction of E2F targets upon E2F stimulation. Expression levels of the E2F targets PCNA, cyclin E1 (CCNE1), and CDC6 upon E2F3 induction was assessed by quantitative PCR, normalized against GAPDH, and the not-induced samples (t = 0) set as 1.0. (C) Expression of the ER-E2F3 fusion protein throughout the assay was assessed at the indicated times, and vinculin was used as a loading control.