Figure 1.

The gypsy insulator prevents enhancer stimulation in an Su(Hw)-dependent manner. (Left) The genes shown are drawn to scale. All plasmids carry the firefly luciferase reporter gene (gray box) under the control of the minimal promoter (−203 to +18) of the D. affinidisjuncta Adh gene (thick line and small arrow). The 4.4-kb ALE is represented by a large curved arrow. Triangles indicate the gypsy insulator. Transient transformation was performed by injecting plasmid mixtures, containing equimolar amounts of the experimental plasmid and an ADH-encoding control plasmid, into the ventral midline of embryos (see Materials and Methods). (Right) The bars represent relative expression of genes (ratios of luciferase activity to ADH activity) normalized to that of a gene carrying a similarly sized fragment of bacteriophage λ DNA instead of the ALE. The shaded bars show results obtained with the standard Adh-null strain, which carries a wild-type su(Hw) gene. The open bars show results for the Adh-null, su(Hw)^f/su(Hw)^v strain, which contains low levels of Su(Hw) protein. Bars represent means ± SE for five independent samples for each gene normalized relative to the value obtained for the control gene in the same genetic background. In addition, numerical values are given for genes having low levels of expression that are not readily evaluated graphically.