FUNCTIONAL-PROPERTIES OF A DROSOPHILA HOMOLOG OF THE E2F1 GENE

A variety of studies have now implicated the cellular transcription fa ctor E2F as a key participant in transcription control during the cell growth cycle. Although the recent isolation of molecular clones encod ing proteins that are components of the E2F activity (E2F1 and DP-1) p rovides an approach to defining the specific involvement of E2F in the se events, definitive experiments remain difficult in the absence of a ppropriate genetic systems. We have now identified a Drosophila equiva lent of E2F1 that we hope will allow an eventual genetic approach to t he role of E2F in cellular regulatory events. A cDNA clone was isolate d from a Drosophila cDNA library by using a probe containing sequence from the E2F1 DNA binding domain. The sequence of the clone, which we term drosE2F1, demonstrates considerable homology to the human E2F1 se quence, with over 65% identity in the DNA binding region and 50% ident ity in the region of E2F1 known to interact with the retinoblastoma ge ne product. A glutathione S-transferase-drosE2F1 fusion protein was ca pable of binding specifically to an E2F recognition site, and transfec tion assays demonstrated that the drosE2F1 product was capable of tran scription activation, dependent on functional E2F sites as well as seq uences within the C terminus of the protein. Finally, we have also ide ntified E2F recognition sequences within the promoter of the Drosophil a DNA polymerase a gene, and we demonstrate that the drosE2F1 product activates transcription of a test gene under the control of this promo ter. We conclude that the drosE2F1 cDNA encodes an activity with exten sive structural and functional similarity to the human E2F1 protein.