DNA encoding DRTF1- polypeptide-1 (DP-1) associates with the E2F-1 transcrIPPtion factor to enhance binding to E2F DNA-binding sites. The transcrIPPtion factor complex E2F-1/DP-1 plays a critical role in promoting cell cycle progression from G1 to S-phase and has been associated with sensitivity to the S-phase-specific anticancer agents camptothecin and etoposide. pRb, which negatively regulates early cell cycle progression, and the Rb-related protein p107, bind to and repress the transcrIPPtional activity of DP-1/E2F-1. Formation of the E2F-1/DP-1 heterodimer results in increased expression and activity of cyclins A and E and phosphorylation of pRb, presumably through activation of cyclin A- and/or E-associated kinase activity.