Evolutionary conserved mechanism of transcriptional repression by even-skipped.

Even-skipped (Eve) is a transcriptional repressor involved in segment formation in Drosophila melano-gaster. In order to gain further insights into the mechanism of action of Eve we tested whether it would function as a transcriptional repressor in mammalian cells. We found that Eve was indeed a potent repressor in two different mammalian cell types and at several promoters. In vitro transcription assays confirmed that Eve directly represses transcription initiation when specifically targeted to a promoter. We also found that, unlike the case with transcriptional activators, Eve does not repress transcription synergistically. Analysis of the effect of Eve on preinitiation complex assembly in a crude HeLa cell nuclear extract demonstrated that the Eve repression domain functions by preventing the assembly of TFIID with the promoter. Our data support the hypothesis that Eve contains an active repression domain that functions specifically to prevent preinitiation complex formation.