Cloning and functional expression of a cDNA encoding a metabolic acyl-CoA delta 9-desaturase of the cabbage looper moth, Trichoplusia ni

Acyl-CoA delta9-desaturases play essential roles in fatty acid metabolism and the regulation of cell membrane fluidity. In this research, a cDNA sequence was obtained from Trichoplusia ni adult fat body mRNA by using RT-PCR with degenerate primers based on other characterized delta9-desaturase sequences. The remainder of the sequence was amplified using 3'- and 5'-RACE. A 1439 bp cDNA reconstructed from three overlapping PCR products contains an ORF encoding a 353-amino acids (aa) protein that shows clear homology (greater than 50% aa identity and greater than 65% aa similarity to characterized insect and vertebrate desaturases). The ORF of this cDNA was subcloned into an expression vector, which relieved the unsaturated fatty acid (UFA) auxotrophy of a desaturase-deficient yeast strain following genetic transformation. The newly characterized desaturase from T. ni produced fatty acids delta9-16 and delta9-18 in a 1:6 ratio, compared to a 5:1 ratio, respectively, with the yeast delta9 desaturase. A Northern blot hybridization and a RT-PCR experiment showed that temporal and tissue-specific patterns of expression of the corresponding mRNA are distinct from those of the delta11 -desaturase mRNA present in the pheromone glands of adult females. Based on its homology to other desaturases, the widespread distribution of its corresponding mRNA in various tissues, and its functional assay, we conclude that this cDNA encodes the apoprotein corresponding to the desaturase component of the metabolic delta9-desaturase complex of T. ni.