Molecular cloning and characterization of Drosophila ornithine aminotransferase gene

The cDNA encoding the Drosophila ananassae ornithine aminotransferase (OAT, EC 2.6.1.13) precursor has been cloned and characterized. The predicted OAT protein sequence is 433 amino acids long with a molecular mass of 47,352 Da and is highly homologous to a mammalian OAT, which is a mitochondrial matrix enzyme and is matured by processing of its amino terminal presequence peptide. The Drosophila OAT has characteristics of leader peptides present in mitochondrial proteins. Immunoblotting experiments using polyclonal antibodies against the partial sequence of the OAT protein revealed that the OAT monomer has a molecular mass of 44 kDa. These results suggest that the Drosophila OAT is also processed and localized in the mitochondria. Quantitation of the OAT mRNA and measurement of the OAT activity during fly development show that OAT is expressed at high levels in the fat body of the third instar larvae in both D. ananassae and D. melanogaster.