Glycerol-3-phosphate o-acyltransferase (GPAT) participates in the first step of oil biosynthesis and is expected to play a key role in altering the quantity of long-chain polyunsaturated fatty acids (PUFAs) produced in oils of oleaginous organisms. The present application provides a nucleic acid fragment isolated from Mortierella alpina encoding a GPAT that is suitable for use in the manufacture of oils enriched in omega fatty acids in oleaginous organisms. Most desirably, the substrate specificity of the instant GPAT 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.