Partial characterization of a fatty acid desaturase gene in Drosophila melanogaster.

The open reading frame of a gene encoding a protein homologous to vertebrate fatty acid desaturases has been characterized in Drosophila melanogaster. This is the first description of a desaturase sequence in insects. Two cDNAs were cloned: the combined 1.5 kb nucleotide sequences indicate that the gene encodes a polypeptide of 383 amino acid residues with a high sequence similarity to the well defined delta 9 desaturases from rat and yeast and desaturases from carp and tick. The Drosophila protein contains two histidine cluster motifs (HXXHH) and two hydrophobic regions which are conserved among all desaturases, whereas the amino and carboxy ends look more variable. The desaturase gene seems to be expressed in adults at a low level, with a greater prevalence in females than in males. Two genomic sequences have been amplified by polymerase chain reaction (PCR), and have a very similar open reading frame but a different organization; one with three introns and the other without introns. Both seem to correspond to two distinct genes and have been named "desat locus". They are localized to a single locus, 87C, on the right arm of the third chromosome. The possible involvement of the desat product in the biosynthesis of D. melanogaster contact pheromones is discussed.