MOLECULAR AND BIOCHEMICAL-CHARACTERIZATION OF THE AANAT1 (DAT) LOCUS IN DROSOPHILA-MELANOGASTER - DIFFERENTIAL EXPRESSION OF 2 GENE-PRODUCTS

In insects, arylalkylamine N-acetyltransferases (AANATs) have been imp licated in several physiological processes, including sclerotization, inactivation of certain neurotransmitters, and, similar to the functio n in vertebrates, catalysis of the rate-limiting step in melatonin bio synthesis. Here, we report an extensive biochemical and functional ana lysis of the products of the aaNAT1 gene of Drosophila melanogaster, T he aaNAT1 gene generates two transcripts through alternative first-exo n usage, These transcripts are under tissue-specific and developmental control and encode proteins which differ in their N-terminus with res pect to their starting methionine, The more abundant isoform, AANAT1b, is first expressed during late embryogenesis in the brain, the ventra l nerve cord, and the midgut; in adults, AANAT1b is still detectable i n the brain and midgut, The less abundant isoform, AANAT1a, appears on ly during late pupal stages and in adults is found predominantly in th e brain. We demonstrate that the mutation Dat(lo) represents a hypomor phic allele of aaNAT1b, in which an insertion of two transposable elem ents, MDG412 and blastopia, has occurred within the first intron of th e gene, Using a deficiency which removes the aaNAT1 gene, we provide e vidence that aaNAT1 is not essential for the process of sclerotization , Furthermore, neither of the two enzyme isoforms shows circadian regu lation of RNA or protein levels. The differing levels of abundance and distinct developmental control of AANAT1a and AANAT1b suggest differe nt in vivo functions for these two enzymes.