MULTIPLE PROTEINS INTERACT WITH THE FUSHI-TARAZU PROXIMAL ENHANCER

The expression of the Drosophila segmentation gene fushi tarazu (ftz) is controlled at the level of transcription. The proximal enhancer, lo cated approximately 3.4 kb upstream of the transcription start site, d irects lacZ fusion gene expression in a ftz-like seven-stripe pattern in transgenic fly embryos. We have taken a biochemical approach to ide ntify DNA-binding proteins that regulate ftz gene expression through t he proximal enhancer. DNase I footprinting and methylation interferenc e experiments with staged Drosophila embryo nuclear extracts identifie d nine protein binding sites in the proximal enhancer. Ten different s equence-specific DNA-binding complexes that interact with eight of the se sites were identified. Some interact with multiple sites, while oth ers bind to single sites in the enhancer. Two of the complexes that in teract with multiple sites appear to contain the previously described ftz regulators, FTZ-F1 and TTK/FTZ-F2. These in vitro studies allowed us to narrow down the proximal enhancer to a 323-bp DNA fragment that contains all of the protein binding sites. Expression directed by this minimal enhancer element in seven ftz-like stripes in transgenic embr yos is identical to that directed by the full-length enhancer. Interna l deletions of several sites abolish reporter gene expression in vivo. Thus, the ftz proximal enhancer, like other cell-type-specific eukary otic enhancers, interacts with an array of proteins that are expected to mediate the establishment, maintenance, and repression of transcrip tion of the ftz gene in seven stripes in the developing embryo.