The Drosophila even-skipped (eve) gene is expressed in seven stripes in the segmentation pattern of the embryo. A sequence segment of 8 kb 5' to the transcription start site (shown as 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 2 expression directed by regulatory sequences in the region 1.7 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 1.7-kb region of the 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-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?

The majority of this chapter focused on gene regulation at the transcriptional level, but the quantity of functional protein product in a cell can be regulated in many other ways as well. Discuss possible reasons why transcriptional regulation or posttranscriptional regulation may have evolved for different types of genes.

Microbiologists describe the processes of transcription and translation as 'coupled' in bacteria. This term indicates that a bacterial mRNA can be undergoing transcription at the same moment it is also undergoing translation. Is coupling of transcription and translation possible in single-celled eukaryotes such as yeast? Why or why not?

Using the components in the accompanying diagram, design regulatory modules (i.e., enhancer/silencer modules) required for 'your' gene to be expressed only in differentiating (early) and differentiated (late) liver cells. Answer the three questions presented below by describing the roles that activators, enhancers, repressors, silencers, pioneer factors, insulators, chromatin remodeling complexes, and chromatin readers, writers, and erasers will play in the regulation of expression of your gene, that is, what factors will bind and be active in each case? Specify which transcription factors need to be pioneer factors. How will expression be prevented in other cell types?