May play an important role in the fine-tuning of both major E2F1 activities, the regulation of the cell-cycle and the induction of apoptosis. Promotes S-phase entry, and inhibits p14(ARP) expression (By similarity). Interacts with E2F1. The C-terminal half binds the N-terminal of E2F1. Also interacts with E2F2 and E2F3, but not E2F4.