pRB contains an E2F1-specific binding domain that allows E2F1-induced apoptosis to be regulated separately from other E2F activities.

The interaction between pRB and E2F is critical for control of the cell cycle and apoptosis. Here we report that pRB contains two distinct E2F binding sites. The previously identified E2F binding site on pRB is necessary for stable association with E2Fs on DNA. A second E2F interaction site is located entirely within the C-terminal domain of pRB and is specific for E2F1. E2F1/pRB complexes formed through this site have low affinity for DNA, but the interaction is sufficient for pRB to regulate E2F1-induced apoptosis, and E2F1 loses the ability to interact with this site following DNA damage. These results show that pRB interacts with individual E2F proteins in different ways and suggest that pRB's regulation of E2F1-induced apoptosis is physically separable from its transcriptional control of other E2F proteins.