THE ADENOSINE2 GENE OF DROSOPHILA-MELANOGASTER ENCODES A FORMYLGLYCINEAMIDE RIBOTIDE AMIDOTRANSFERASE

Drosophila melanogaster genomic DNA spanning an adenosine2 gene rearra ngement breakpoint (in cytological map region 26B1-2) was cloned and a composite ade2 base sequence was derived from this DNA and from a cor responding cDNA. Based on genetic evidence, the ade2 gene is thought t o encode the purine biosynthetic enzyme formylglycineamide ribotide am idotransferase (FGARAT). The cDNA hybridizes to a 4.8-kb message that encodes a 1354 amino acid polypeptide with extensive similarity to Esc herichia coli FGARAT. The D. melanogaster FGARAT amino acid sequence i s considerably more like that of the E. coli enzyme than is the FGARAT of B. subtilis, which has two polypeptides with, collectively, 969 am ino acids. It is suggested that the taxonomically anomalous similarity between the eukaryotic FGARAT and that from E. coli may indicate hori zontal exchange of genetic material. On the basis of substantially gre ater conservation of sequences shared by all three species compared wi th those present only in E. coli and D. melanogaster, we suggest that no radical alteration of enzymatic function accompanied the transition between the single-gene and the two-gene state.