Cloning and dosage compensation of the 6‐phosphogluconate dehydrogenase gene (Pgd⁺) of Drosophila melanogaster

Using a heterologous rat cDNA probe, we have identified a 14.7 kbp Drosophila melanogaster genomic clone containing the X‐linked gene Pgd⁺, which encodes the enzyme 6‐phosphogluconate dehydrogenase (6PGD). We used in situ hybridization to larval polytene chromosomes, a somatic transient expression assay for enzyme activity, and the rescue of the lethal Pgd⁻ phenotype by germline transformation to verify the identity of the gene. A 7.4 kbp fragment including the gene and approximately 1.2 kbp of upstream and 1.8 kbp of downstream sequences was relocated to autosomal ectopic sites by germline transformation; this transduced gene exhibits levels of enhanced activity in males comparable to those of the indigenous gene at its normal X chromosome locus. We conclude that the sequences responsible for dosage compensation of Pgd⁺ are included in this fragment.