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 bee n implicated in the control of genes essential for cell cycle progress ion, Regulation of E2F function is finely tuned by the retinoblastoma tumor suppressor gene product and a small family of related ''pocket p roteins,'' with the participation of a number of cyclins and cyclin-de pendent kinases. Perturbations of this regulatory network can lead to oncogenic transformation and, in certain systems, to the loss of the a bility to maintain terminal differentiation. We describe here the clon ing, structural characterization, and tissue expression pattern of a n ew member of the E2F family, E2F-5. We show that this protein is highl y 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 E2 F-5 mRNA among adult rat tissues and the temporal pattern of its expre ssion during the cell cycle of vascular smooth muscle cells are distin ctly different from that of E2F-1, The structural divergence between t he two branches of the E2F family may thus reflect participation in di fferent regulatory networks,