Identification of Δ12-fatty acid desaturase from arachidonic acid-producing Mortierella fungus by heterologous expression in the yeast Saccharomyces cerevisiae and the fungus Aspergillus oryzae

Based on the sequence information for the omega 3-desaturase genes (from Brassica napus and Caenorhabditis elegans), which are involved in the desaturation of linoleic acid (Delta 9, Delta 12-18 : 2) to a-linolenic acid (Delta 9, Delta 12, Delta 15-18 : 3, a cDNA was cloned from the filamentous fungal strain, Mortierella alpina 1S-4, which is used industrially to produce arachidonic acid. Homology analysis with protein databases revealed that the amino acid sequence showed 43.7% identity as the highest match with the microsomal omega 6-desaturase (from Glycine max, soybean), whereas it exhibited 38.9% identity with the microsomal omega 3-desaturase (from soybean). The evolutionary implications of these enzymes will be discussed. The cloned cDNA was confirmed to encode a a12-desaturase, which was involved in the desaturation of oleic acid (Delta 9-18 : 1) to linoleic acid, by its expression in both the yeast Saccharomyces cerevisiae and the fungus Aspergillus oryzae. Analysis of the fatty acid composition of yeast and fungus transformants demonstrated that linoleic acid (which was not contained in the control strain of S. cerevisiae) was accumulated in the yeast transformant and that the fungal transformant contained a large amount of linoleic acid (71.9%). Genomic Southern blot analysis of the transformants with the Mortierella Delta 12-desaturase gene as a probe confirmed integration of this gene into the genome of A. oryzae. The M. alpina 1S-4 Delta 12-desaturase is the first example of a cloned nonplant Delta 12-desaturase.