The present invention relates to a protein having an activity to promote fatty acid chain elongation, a polynucleotide encoding the same, etc. The present invention provides, for example, a polynucleotide containing the nucleotide sequence shown in SEQ ID NO: 1 or 4, a polynucleotide encoding a protein which consists of the amino acid sequence shown in SEQ ID NO: 2, an expression vector and a transformant, each containing such a polynucleotide, a method for preparing lipids or fatty acids by using such a transformant, or a food or the like containing lipids or fatty acids prepared by such a method.
