Cloning of Δ12-and Δ6-desaturases from Mortierella alpina and recombinant production of γ-linolenic acid in Saccharomyces cerevisiae

Two cDNA clones with homology to known desaturase genes were isolated from the fungus Mortierella alpina. The open reading frame in one clone encoded 399 amino acids and exhibited Delta 12-desaturase activity when expressed in Saccharomyces cerevisiae in the presence of endogenous fatty acid substrate oleic acid. The insert in another clone contained an open reading frame encoding 457 amino acids and exhibited Delta 6-desaturase activity in S. cerevisiae in the presence of exogenous fatty acid substrate linoleic acid. Expression of the Delta 12-desaturase gene under appropriate media and temperature conditions led to the production of linoleic acid at levels up to 25% of the total fatty acids in yeast. When linoleic acid was provided as an exogenous substrate to the yeast cultures expressing the Delta 6-desaturase activity, the level of gamma-linolenic acid reached 10% of the total yeast fatty acids. Co-expression of both the Delta 6- and Delta 12-desaturase cDNA resulted in the endogenous production of gamma-linolenic acid. The yields of gamma-linolenic acid reached as high as 8% of total fatty acids in yeast.