The present invention relates to a polynucleotide encoding an omega 3 (ω-3) desaturase from Pythium irregulare with specificity to long chain polyunsaturated omega 6 (ω-6) fatty acids as well as a vector containing the polynucleotide, and a host cell containing the vector or the polynucleotide. Moreover, the present invention pertains to a polypeptide encoded by the polynucleotide, antibodies against the polypeptide as well as a method for the manufacture of the polypeptide. Further, encompassed by the present invention are transgenic non-human organisms. Finally, the present invention relates to methods for the manufacture of compounds and oil- fatty acid-, or lipid-containing compositions.
