FIG 8.

Control of cell proliferation by TAg in the absence of activator E2Fs. (A) Depletion of all three activator E2Fs has a double effect. First, it leads to p53-mediated cell cycle arrest or apoptosis; second, the promoters of the genes driving cell proliferation are occupied by the p130/E2F4 repressive complexes. The overall result is a block in the cell cycle. (B) TAg binds p53 and prevents expression of p53 target genes, thus impeding apoptosis. Simultaneously, TAg disrupts p130/E2F repressor complexes, removing them from the promoters of cell cycle genes. The expression of E2F target genes could then occur solely due to the absence of repression (1) or to the recruitment of an unknown activator “X” to replace E2F1-2-3 (2).