THE DROSOPHILA-COPIA RETROTRANSPOSON CONTAINS BINDING-SITES FOR TRANSCRIPTIONAL REGULATION BY HOMEOPROTEINS

We have identified in the 5' untranslated region of the Drosophila cop ia retrotransposon, 3' to the left LTR, a sequence for transcriptional regulation by homeoproteins. Co-transfection assays using expression vectors for homeoproteins and reporter vectors containing the lacZ gen e under the control of either the entire copia LTR with 5' untranslate d sequence, or a minimal heterologous promoter flanked with a 130bp fr agment containing the copia untranslated region, disclosed both positi ve and negative modulations of promoter activity in Drosophila cells i n culture: a 5 - 10 fold decrease with engrailed, even-skipped and zer knullt in DH33 cells, and a 10 - 30 fold increase with fushi tarazu an d zerknullt in Schneider II cells. In all cases, the regulatory effect s were abolished with reporter plasmids deleted for a 58 bp fragment e ncompassing the putative homeoprotein binding sites. Mobility shift as says with a purified homeodomain-containing peptide demonstrated direc t interaction with the 58bp fragment, with an affinity in the 1 - 10nM range as reported with the same peptide for other well characterized homeodomain binding regulatory sites. Footprinting experiments with th e extended LTR demonstrated protection of 'consensus' sequences, locat ed within the 58bp fragment. These homeodomain binding sites could be involved in the developmental regulation of the copia retrotransposon.