The invention provides nucleic acid molecules which encodes a novel fatty acid desaturase, KCS, KCR and/or LACS from Thraustochytrium aureum and Sphaeroforma arctica. The invention also provides recombinant expression vectors containing the nucleic acid molecules, host cells into which the expression vectors have been introduced, and methods for large-scale production of long chain polyunsaturated fatty acids (LCPUFAs), e.g., ARA, EPA and DHA and for screening for delta-4 desaturases.