The present invention relates to an acyl-CoA synthetase homolog protein from microorganisms of the genus Mortierella, a polynucleotide encoding the protein, and so on. The invention provides polynucleotides comprising an acyl-CoA synthetase homolog protein gene from, e.g., Mortierella alpina, expression vectors comprising these polynucleotides and transformants thereof, a method for producing lipids or fatty acids using the transformants, food products containing the lipids or fatty acids produced by the method, etc.
