Complementation cloning and characterization of the pyrroline 5-carboxylate reductase gene from Drosophila melanogaster

The first insect cDNA and genomic sequences encoding pyrroline 5-carboxylat e reductase (EC 1.5.1.2) have been isolated from Drosophila melanogaster. T he cDNA sequence M,as identified by interspecies complementation of an E. c oli proline auxotroph and encodes a protein 280 amino acids in length with 25-41% identity to pyrroline 5-carboxylate reductases isolated from other o rganisms. The corresponding gene is single copy and is located at cytologic al position 91E-F, and in one of the PI clones in that region. With a singl e 61-bp intron, and an impressively small 135- to 200-bp region that presum ably acts as a bidirectional promoter, the gene itself shows remarkable eco nomy. The calculated molecular weight of 29,700 predicts that the native en zyme is likely an octomer. Sequencing of the promoter region and Expression studies, as well as the known function of the enzyme in redox regulation a nd the high levels of free proline in insects, suggest that this housekeepi ng gene encodes an enzyme with a crucial role in intermediary metabolism.