Figure 7.

A novel picture of E2F transcriptional regulation. (A) The genes regulated by dE2F1 activation and dE2F2 repression are required for the regulation of distinct cellular functions. dE2F1 is required to activate the expression of genes involved in cell cycle progression. dE2F2, on the other hand, is required to repress a variety of tissue-specific genes involved in differentiation. The previously reported gain-of-function of dE2F2 at cell cycle promoters in the absence of dE2F1 is represented by the dotted arrow. (B) The mechanism of differential E2F regulation. The expression of dE2F1-dependent transcripts is coupled with a burst of dE2F1 expression at the G1/S transition of the cell cycle and with high G1/S Cdk activity. dE2F2-dependent transcripts are not activated by dE2F1, and dE2F2/RBF complexes present at their promoters are not disrupted by G1/S Cdks. Their expression requires tissue-specific transcription factors (X) and/or developmentally regulated signals.