The hiiragi (hrg) gene plays a key role in the development of the wing margin in Drosophila melanogaster. A mutation in the hrg gene resulted in a decrease in the level of the hrg transcript and was associated with a notched wing phenotype. We report here that the hrg gene encodes a poly(A) polymerase (PAP). The bovine cDNA for PAP type II reversed the phenotype due to mutation of the hrg gene, suggesting that hrg might encode a functional homolog of PAP. A mutation that reduced the enzymatic activity of Hrg failed to reverse the phenotype of hrg mutants, suggesting that the enzymatic activity of Hrg was required to rescue the wing phenotype. The levels of expression of wingless and cut at the presumptive wing margins were reduced in the late third-instar larvae of hrg mutants. These results suggest that the product of hrg is required for the normal expression of a series of genes in this region. Our results provide the first evidence that a PAP in Drosophila plays a key role in the early development of the wing margin, acting to regulate the specific expression of a series of genes via, perhaps, control of the processing of the 3' ends of transcripts.