Drosophila P-element transposase is a transcriptional repressor in vitro.

Mobility of P transposable elements in Drosophila melanogaster depends on the 87-kDa transposase protein encoded by the P element. Transposase recognizes a 10-base-pair DNA sequence that overlaps an A + T-rich region essential for transcription from the P-element promoter. We report here that transposase represses transcription from the P-element promoter in vitro. This transcriptional repression is blocked by prior formation of an RNA polymerase II transcription complex on the template DNA. Binding of transposase on the P-element promoter is blocked by prior binding of either the Drosophila RNA polymerase II complex or the yeast transcription factor TFIID. These data suggest that transposase represses transcription by preventing assembly of an RNA polymerase II complex at the P-element promoter.