Identification of Δ5-desaturase from Mortierella alpina by heterologous expression in bakers' yeast and canola

A DNA fragment with homology to Delta 6-desaturases from borage and cyanobacteria was isolated after polymerase chain reaction amplification of Mortierella alpina cDNA with oligonucleotide primers corresponding to the conserved regions of known Delta 6-desaturase genes. This fragment was used as a probe to isolate a cDNA clone with an open reading frame encoding 446 amino acids from a M. alpina library, Expression of this open reading frame from an inducible promoter in Saccharomyces ces cerevisiae in the presence of various substrates revealed that the recombinant product had Delta 5-desaturase activity. The effects of growth and induction conditions as well as host strain on activity of the recombinant Delta 5-desaturase in S. cerevisiae were evaluated. Expression of the M. alpina Delta 5-desaturase cDNA in transgenic canola seeds resulted in the production of taxoleic acid (Delta 5,9-18:2) and pinolenic acid (Delta 5,9,12-18: 3), which are the Delta 5-desaturation products of oleic and linoleic acids, respectively.