ARF dissociates the E2F4–DP1 interaction. (A) TKO MEFs or (B) ARF-null MEFs were infected with control or ARF-expressing adenovirus for 16 h. Cell extracts (1 mg) were immunoprecipitated (IP) using the E2F4 antibody, and the immunoprecipitates were subjected to Western blot analysis using the DP1 antibody. The levels of E2F4, DP1 and ARF in the extracts (0.1 mg) of the infected cells are also shown. Ad, adenovirus; ARF, alternative reading frame; CDK2, cyclin-dependent kinase 2; DKO, double knockout; DP1, DRTF polypeptide 1; E2F4, E2F transcription factor 4; MEF, mouse embryonic fibroblast; TKO, triple knockout.