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. Interacts with E2F1. The C-terminal half binds the N-terminal of E2F1. Also interacts with E2F2 and E2F3, but not E2F4. Ubiquitously expressed. Highest levels in heart, placenta, skeletal muscle and pancreas. Lower levels in brain, lung and kidney. In the brain, expressed in all regions with high levels in the cerebellum and cerebral cortex. Expressed in COS1 and transformed skin fibroblasts. During the cell cycle, expression disappears during mitosis.