Chapter 14, Problem 27P

The Drosophila even $\text{-}$ skipped (eve) gene is expressed in seven stripes in the segmentation pattern of the embryo. A sequence segment of $\text{8 kb 5'}$ to the transcription start site (shown as $+1$ in the accompanying figure) is required to drive expression of a reporter gene (lacZ) in the same pattern as the endogenous eve gene. Remarkably, expression of most of the seven stripes appears to be specified independently, with stripe $\text{2}$ expression directed by regulatory sequences in the region $\text{1}\text{.7 kb 5'}$ to the transcription start site. To further examine stripe $2$ regulatory sequences, you create a series of constructs, each containing different fragments of the $\text{1}\text{.7-kb}$ region of $\text{5'}$ sequence. In the lower part of the figure, the bars at left represent the sequences of DNA included in your reporter gene constructs, and the $+$ and $-$ signs at right indicate whether the corresponding eve $\text{-}$ lacZ reporter gene directs stripe $2$ expression in Drosophila embryos transformed through P element mediation. How would you interpret the results $—$ that is, where do the regulatory sequences responsible for stripe $2$ expression reside?