E2F-1 (also known as tran-scription factor E2F-1, Retinoblastoma binding protein 3, RBBP-3, PRB-binding protein E2F-1, PBR3, Retinoblastoma-associated protein 1 and RBAP-1) is a transcription activator that binds DNA cooperatively with DP proteins through the E2 recognition site, 5'-TTTC[CG]CGC-3'. The E2F family plays a crucial role in the control of cell cycle and action of tumor suppressor proteins and is also a target of the transforming proteins of small DNA tumor viruses. The E2F proteins contain several domains con-served through evolution that are found in most members of the family. These domains include a DNA binding domain, a dimerization domain that determines interaction with the differentiation regulated transcription factor proteins (DP), a transactivation domain enriched in acidic amino acids, and a tumor suppressor protein association domain which is embedded within the transactivation domain. This protein as well as E2F2 and E2F3 have an additional cyclin binding domain. This protein binds preferentially to retinoblastoma protein pRB in a cell-cycle dependent manner and mediates both cell proliferation and p53-dependent/independent apoptosis. Increased nuclear expression of this protein has been reported in a variety of cancers.