Transcriptional control of the drosophila segmentation gene fushi tarazu

The Drosophila segmentation gene fushi tarazu (ftz) is expressed in a characteristic pattern of seven stripes during early embryogenesis. The promoter sequences sufficient to direct this stripe pattern are located within the 670 base pairs (bp) proximal to the ftz transcriptional start site. When we extract nuclear proteins from 0-12 hour Drosophila embryos, we find sequence-specific DNA binding proteins that recognize multiple sites within the 670 by zebra stripe promoter. This observation suggests that the control of ftz zebra stripe expression may require a complex array of transcriptional regulators. The results of our P element-mediated transformation experiments using ftz promoter/ [beta]-galactosidase fusion genes confirm this notion. They demonstrate that the zebra stripe promoter contains multiple, distinct activator and repressor recognition elements responsible for the formation of ftz stripes. The transformation studies also reveal that a pattern of general activation, that is, a continuous band of gene expression throughout the germ band, can be generated when repressor recognition sites are deleted from the fusion gene promoter and activator sites are retained. This result strongly supports a mechanism for ftz stripe formation involving general transcriptional activation and localized repression. Studies with constructs in which individual protein binding sites have been deleted or added to the ftz promoter correlate protein recognition elements with regulatory functions. We characterized two distinct interband repressor sites and two distinct general activator sites with this approach. One activator site recognizes the product of the homeobox gene caudal (cad); the other contains a DNA sequence motif found in the cis-activators of a number of Drosophila genes. As would be expected for general activators, both these sites are able to mediate expression throughout most of the germ band. We also demonstrate that when multiple copies of two distinct repressor recognition sites are independently ligated to a portion of the ftz promoter, they transform the continuous band of gene expression generated by a group of endogenous cis-activators into the characteristic seven stripe pattern of ftz expression. Finally, we find that multiple copies of these repressor elements are more capable of mediating repression than single copies