The I factor is a LINE-like transposable element in the genome of Drosophila melanogaster. Transposition of the I factor occurs by reverse transcription of an RNA intermediate and is activated in the germline of female progeny of crosses between males of an inducer strain that contains complete elements and females of a strain that does not, reactive strain, resulting in a phenomenon called I-R hybrid dysgenesis. Previous data have shown that the promoter of the I factor lies between nucleotides 1 and 30. Expression from this promoter is regulated by sequences between nucleotides 41 and 186 that function as an enhancer. The work present in this thesis has identified within this region a sequence called site 1, encompassing nucleotides 138-157, that is recognised by a sequence specific binding protein. This binding protein is present in ovaries and non-ovarian tissues of both inducer and reactive strains. Site 1 is required for basal promoter activity as well as the enhanced expression in the ovaries of reactive females. We suggest that the level of expression form the I factor promoter is dependent on the ratio of site 1 and its sequence specific binding factor or other proteins that interact with it.