Structural characterization and specificity of expression of E2F-5: a new member of the E2F family of transcription factors.

: Members of the E2F gene family are transcription factors that have been implicated in the control of genes essential for cell cycle progression. Regulation of E2F function is finely tuned by the retinoblastoma tumor suppressor gene product and a small family of related "pocket proteins," with the participation of a number of cyclins and cyclin-dependent kinases. Perturbations of this regulatory network can lead to oncogenic transformation and, in certain systems, to the loss of the ability to maintain terminal differentiation. We describe here the cloning, structural characterization, and tissue expression pattern of a new member of the E2F family, E2F-5. We show that this protein is highly conserved between human and rat but exhibits considerable divergence from E2F-1, E2F-2, or E2F3. Together with the recently reported E2F-4, E2F-5 defines a new branch of the E2F family. The distribution of E2F-5 mRNA among adult rat tissues and the temporal pattern of its expression during the cell cycle of vascular smooth muscle cells are distinctly different from that of E2F-1. The structural divergence between the two branches of the E2F family may thus reflect participation in different regulatory networks.