REPRESSION OF AP-1-STIMULATED TRANSCRIPTION BY C-ETS-1

The transcriptional activities of c-Ets-1 and v-Ets and their function al interaction with the AP-1 factor c-Jun were investigated. Several r ecombinant Ets proteins were produced and purified either from bacteri a or from insect cells. Plasmid DNAs that contained the polyoma virus enhancer Ets/AP-1 element were used as templates for in vitro transcri ption assays in the presence of HeLa nuclear extract and Various combi nations of the Jun and Ets proteins. Under these conditions full-lengt h c-Ets-1 on its own does not markedly influence transcription but abo lishes the strong transcriptional stimulation normally elicited by Jun . This repression depends on the Ets-binding site and on specific feat ures of c-Ets-1 structure, as both v-Ets and a natural splicing varian t c-Ets-1 (Delta VII) fail to inhibit Jun activity. These findings sug gest that c-Ets may act both as a transcriptional repressor or activat or depending on promoter context and splicing pattern.