Cloning of Δ12- and Δ-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 Δ12-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 Δ6-desaturase activity in S. cerevisiae in the presence of exogenous fatty acid substrate linoleic acid. Expression of the Δ12-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 Δ6-desaturase activity, the level of γ-linolenic acid reached 10% of the total yeast fatty acids. Co-expression of both the Δ6- and Δ12-desaturase cDNA resulted in the endogenous production of γ-linolenic acid. The yields of γ-linolenic acid reached as high as 8% of total fatty acids in yeast.