The transcription factor E2F consists of a family of proteins that bind to the sequence TTTCGCGC and regulate the expression of various cellular and viral promoters. E2F binds to DNA as homodimers or as heterodimers in association with a protein, DP1 (for dimerization partner 1). E2F-DP1 heterodimers bind more efficiently than homodimers to DNA, retinoblastoma gene product as well as the adenovirus E4 protein and DP1 can stimulate transcription from E2F sites in a synergistic fashion. Here we describe the cloning and characterization of a novel human DP gene, DP2, whose product dimerizes efficiently with E2F. Unlike DP1, there appear to be multiple transcripts for DP2 and their distribution appears to vary in different tissues and cell lines. DP2 binds to E2F as detected by in vitro reconstitution assays and an E2F-DP2 heterodimer can bind to DNA in gel-retardation assays. We believe that DP2 also plays a major role in modulating the function of E2F in cell cycle regulation and oncogenesis.