HETERODIMERIZATION OF THE TRANSCRIPTION FACTORS E2F-1 AND DP-1 IS REQUIRED FOR BINDING TO THE ADENOVIRUS E4 (ORF6 7) PROTEIN/

Adenovirus infection leads to E1A-dependent activation of the transcri ption factor E2F. E2F has recently been identified in complexes with c ellular proteins such as the retinoblastoma protein (pRB) and the two pRB family members p107 and p130. E1A dissociates E2F from these cellu lar proteins, and another viral protein, E4 (ORF6/7), can bind to E2F. The binding of E4 to E2F induces the formation of a stable DNA-bindin g complex containing the two proteins, and stimulation of the adenovir us E2 early promoter can occur. Recent studies have shown that E2F is the combined activity of several proteins, and we demonstrate here tha t heterodimerization of two of these proteins, E2F-1 and DP-1, is requ ired for stable binding to E4. This complex is formed independently of DNA binding and requires the C-terminal 20 amino acids of E4. Further more, the binding is dependent on a region of E2F-1 between amino acid s 284 and 358. This region of E2F-1 is conserved in E2F-2 and E2F-3, a nd deletion of this region drastically reduces the transcriptional act ivity of the molecule without affecting DP-1 binding, suggesting that this region of the E2F transcription factors is involved in regulating their activity. Our experiments also demonstrate that pRB binding to the E2F-1/DP-1 heterodimer prevents the formation of an E2F-1/DP-1/E4 complex.