We demonstrated that Mortierella alpina 1S-4 has two Δ6-desaturases, which are involved in the desaturation of linoleic acid to γ-linolenic acid. For one of the two Δ6-desaturases, designated as Δ6I, gene cloning and its heterologous expression in a fungus, Aspergillus oryzae, has previously been reported. In addition, we indicated in this paper that there is an isozyme of the two Δ6-desaturases, designated as Δ6II, in M. alpina 1S-4. The predicted amino acid sequences of the Mortierella Δ6-desaturases were similar to those of ones from other organisms, i.e. borage and Caenorhabditis elegans, and had a cytochrome b₅-like domain at the N-terminus, being different from the yeast Δ9-desaturase, which has the corresponding domain at the C-terminus. The full-length Δ6II cDNA was expressed in A. oryzae, resulting in the accumulation of γ-linolenic acid (which was not detected in the control Aspergillus) up to 37% of the total fatty acids. The analysis of real-time quantitative PCR (RTQ-PCR) showed that the quantity of Δ6I RNA was 2.4-, 9-, and 17-fold higher than that of Δ6II RNA on 2, 3, and 4 days in M. alpina 1S-4, respectively. M. alpina 1S-4 is the first fungus to be confirmed to have two functional Δ6-desaturase genes.

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