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A conserved palindromic sequence (Gpal) in the promoter region of the Drosophila GId directs expression of a heterologous reporter gene in transgenic flies to the anterior spiracular ands of third instar larvae and to the ejaculatory bulb of adult males. The Gldgene is normally expressed at high levels in the anterior spiracular glands but is not expressed in the ejaculatory bulb ofDrosophila melanogaster. However, GMd promoters from other DrosophUa species contain the Gpal element and express glucose dehydrogenase (GLD) in the adult male ejaculatory bulb. A gene fusion composed of the D.melanogasterGl promoter and the lacZ gene is expressed in the anterior spiracular glands of transgenlc larvae. Mutations of the Gpal sequence element in this gene fusion block expression of f-galactosidase in the anterior spiracular gland. Together these experiments demonstrate that Gpal is necessary and sufficient for tissue-specific expression in the anterior spiracular glands. Based upon the tissue distribution and function of GLD, it is spculated that expression of GLD in the anterior spiracular glands represents the ancestral state and that GLD expression in other tissues arose as a fortuitous consequence of a shared combinatorial regulatory network.