CONTROL OF EXPRESSION OF THE I-FACTOR, A LINE-LIKE TRANSPOSABLE ELEMENT IN DROSOPHILA-MELANOGASTER

I factors are LINE-like transposable elements in the genome of Drosoph ila melanogaster. They normally transpose infrequently but are activat ed in the germline of female progeny of crosses between males of a str ain that contains complete elements, an I or inducer strain and female s of a strain that does not, an R or reactive strain. This causes a ph enomenon known as I-R hybrid dysgenesis, We have previously shown that the I factor promoter lies between nucleotides 1 and 30. Here we demo nstrate that expression of this promoter is regulated by nucleotides 4 1-186 of the I factor. This sequence can act as an enhancer as it stim ulates expression of the hsp70 promoter in ovaries in the absence of h eat-shock. Within this region there is a site that is required for pro moter activity and that is recognized by a sequence-specific binding p rotein, We propose that this protein contributes to the enhancer activ ity of nucleotides 41-186 and that reduced I factor expression in indu cer strains is due to titration of this protein or others that interac t with it.