An acyltransferase is provided, suitable for use in the manufacture of microbial oils enriched in omega fatty acids in oleaginous organisms. Specifically, the gene encoding diacylglycerol acyltransferase (DGAT2) has been isolated from Mortierella alpina. This gene encodes an enzyme that participates in the terminal step in oil biosynthesis in fungi and yeast and is expected to play a key role in altering the quantity of long-chain polyunsaturated fatty acids produced in oils of oleaginous organisms. Most desirably, the substrate specificity of the instant DGAT2 will be particularly useful to enable accumulation of long-chain PUFAs having chain lengths equal to or greater than C.sub.20 in oleaginous yeast, such as Yarrowia lipolytica.