Production of Polyunsaturated Fatty Acids by Genetic Engineering of Yeast

In order to study the production system of polyunsaturated fatty acids (PUFA), we genetically engineered a baker’s yeast that did not originally produce PUFA. We produced γ-linolenic acid (GLA) by constructing a heterologous system to express Δ6 fatty acid desaturase (D6d) gene from rat liver into yeast, Saccharomyces cerevisiae. The expression of this gene in the presence of linoleic acid (LA) formed a significant amount of GLA in the host cells. In order to effect the largest expression of the conversion rate from LA to GLA, we set up a dual promoter system, where genes coding for the D6d and an elecron donor protein, cytochrome b5, were coordinately expressed. The desaturation index (GLA/LA) increased significantly by high level expression of cytochrome b5, indicating that this protein is a limiting factor in regular yeast. In addition, we examined a condition for the extra-cellular production of GLA by a fatty acid secretion yeast mutant. By expressing the D6d gene under the control of GAP-DH promoter in the presence of LA, 178 mg/L of GLA was secreted in the medium in 144h.