NUCLEAR-LOCALIZATION OF DP AND E2F TRANSCRIPTION FACTORS BY HETERODIMERIC PARTNERS AND RETINOBLASTOMA PROTEIN FAMILY MEMBERS

E2F is a family of transcription factors implicated in the regulation of genes required for progression through G(1) and entry into the S ph ase. The transcriptionally active forms of E2F are heterodimers compos ed of one polypeptide encoded by the E2F gene family and one polypepti de encoded by the DP gene family. The transcriptional activity of E2F/ DP heterodimers is influenced by association with the members of the r etinoblastoma tumor suppressor protein family (pRb, p107, and p130). H ere the intracellular distribution of E2F and DP proteins was investig ated in transiently transfected Chinese hamster and human cells. In tr ansfected cells, DP-1 did not accumulate in the nucleus unless it was coexpressed with the heterodimeric partners E2F-1, E2F-2, or E2F-3. Do main mapping experiments showed that regions of E2F-1 and DP-1 that ar e required for stable association of the two proteins were also requir ed for nuclear localization of DP-1. Unlike E2F-1, -2, and -3, E2F-4 d id not accumulate in the nucleus unless it was coexpressed with DP-2. p107 and p130, but not pRb, stimulated nuclear localization of E2F-4, either alone or in combination with DP-2. These results indicate that DP proteins preferentially associate with specific E2F partners, and s uggest that the ability of specific E2F/DP heterodimers to localize in the nucleus contributes to the regulation of E2F activity.