THE 5' UNTRANSLATED REGION OF THE I FACTOR, A LONG INTERSPERSED NUCLEAR ELEMENT-LIKE RETROTRANSPOSON OF DROSOPHILA-MELANOGASTER, CONTAINS AN INTERNAL PROMOTER AND SEQUENCES THAT REGULATE EXPRESSION

The I-R system of hybrid dysgenesis in Drosophila melanogaster is controlled by a long interspersed nuclear element-like retroposon, the I factor. Transposition of the I factor occurs at a high frequency only in the ovaries of females produced by crossing males of inducer strains that contain functional I factors with females of reactive strains that lack them. In this study, the 5' untranslated region of the I factor was joined to the chloramphenicol acetyltransferase gene, and activity was assayed in transfected D. melanogaster tissue culture cells and transformed flies. The results have identified a promoter that lies within the first 186 bp of the I factor. Deletion analysis shows that nucleotides + 1 to + 40 are sufficient for high promoter activity and accurate transcription initiation. This region contains sequences that are found in a class of RNA polymerase II promoters that lack both a TATA box and CpG-rich motifs. In transformed flies, high levels of expression from nucleotides + 1 to + 186 are confined to the ovaries of reactive females, suggesting that the promoter is involved in the tissue and cytotype specificity of transposition.