Method for preparing polyunsaturated fatty acids (PUFA) in an organism by (a) introducing any of 20 specific nucleic acid sequences (I), or their equivalents, derivatives or homologs and (b) culturing then harvesting the organisms. Method for preparing polyunsaturated fatty acids (PUFA) in an organism comprises introducing any of 20 specific nucleic acid sequences (I), or their equivalents, derivatives or homologs and culturing then harvesting the organisms. (I) is any of: (a) 12 sequences encoding lysophosphatidylic acid acyltransferase, 3 sequences encoding glycerol-3-phosphate acyltransferases, 3 sequences encoding diacylglycerol acyltransferases or 2 sequences encoding lecithin-cholesterol acyltransferases； (b) equivalents of (A) within the degeneracy of the genetic code； or (c) a derivative of (A) that encodes a protein with at least 40% homology at the amino acid level with proteins encoded by (A) and having equivalent acyltransferase activity. Independent claims are also included for the following: (1) the 20 specified (I), their degenerate equivalents and derivatives, as new compounds； (2) proteins encoded by (I)； (3) gene construct that contains (I)； (4) vector that contains (I) or the construct of (3)； (5) transgenic non-human organisms containing at least one (I), construct of (3) or vector of (4)； and (6) oil, lipid or fatty acid, or their compositions or fragments, containing PUFA and prepared by the new method.
