FIG. 1.

Overview of the experimental approach. To place the hsp70 core promoter under the control of the Gal4p activator, sequences normally found upstream from the TATA box of hsp70 beginning at position −44 were replaced with five binding sites for the yeast Gal4p activator. The fusion of sequences encoding β-galactosidase was made at position +84. Transgenic flies containing this construct were mated with flies that expressed the yeast Gal4p activator. Two Gal4p-expressing lines of flies were used in this study. hsGAL42-1 is a fly line that has the Gal4p gene under the control of the hsp70 heat shock gene promoter. Mz-1087.hx is an enhancer trap fly line that specifically expresses Gal4p in salivary glands. In this case, the Gal4p gene resides on the X chromosome. The salivary glands of third-instar larvae from various matings were analyzed by permanganate genomic footprinting. The glands were dissected from the larvae and treated for 2 min with 40 mM permanganate. Genomic DNA was isolated and heated with piperidine to cleave the DNA backbone at oxidized thymine residues. The pattern of cleavage was then determined by ligation-mediated PCR.