THE ALCOHOL-DEHYDROGENASE GENE IS NESTED IN THE OUTSPREAD LOCUS OF DROSOPHILA-MELANOGASTER

This report describes the structure and expression of the outspread (o sp) gene of Drosophila melanogaster. Previous work showed that chromos omal breakpoints associated with mutations of the osp locus map to bot h sides of the alcohol dehydrogenase gene (Adh), suggesting that Adh a nd the adjacent gene Adh(r) are nested in osp. We extended a chromosom al walk and mapped additional osp mutations to define the maximum mole cular limit of osl as 119 kb. We identified a 6-kb transcript that hyb ridizes to osp region DNA and is altered or absent in osp mutants. Acc umulation of this RNA peaks during embryonic and pupal periods. The os p cDNAs comprise two distinct classes based on alternative splicing pa tterns. The 5' end of the longest cDNA was extended by PCR amplificati on. When hybridized to the osp walk, the 5' extension verifies that Ad h and Adh(r) are nested in osp and shows that osp has a transcription unit of greater than or equal to 74 kb. In situ hybridization shows th at osp is expressed both maternally and zygotically. In the ovary, osp is transcribed in nurse cells and localized in the oocyte. In embryos , expression is most abundant in the developing visceral and somatic m usculature.