Fig. 4. Dissociation of protein-protein interactions in E2F—DNA—protein complexes. Nuclear extracts were prepared from synchronized G₁ and TGF-ß1-induced preapoptotic cells. DNA-binding assays were performed using ³²P-labeled wild-type E2F-specific oligonucleotides with increasing concentrations of sodium deoxycholate from 0.2% to 1.2%. The DNA—protein complexes were analyzed by PAGE as described in Materials and Methods. The position and numerical designation of the ³²P-labeled DNA—protein complexes are indicated on the left. The cell cycle phase from which the nuclear extract was obtained is shown at the top. DOC, sodium deoxycholate; TGF-ß1, preapoptotic nuclear extracts from HuH-7 cells incubated for 72 hours with 1 nM TGF-ß1.