The invention aims at providing a process for producing coenzyme Q.sub.10 efficiently in microorganisms by utilizing a coenzyme Q.sub.10 side chain synthesis gene derived from a fungal species belonging to the genus Aspergillus and genus Leucosporidium. The present invention relates to a DNA having a DNA sequence described under SEQ ID NO:1 and 2 or derived from the above sequence by deletion, addition, insertion and/or substitution of one or several bases and encoding a protein having decaprenyl diphosphate synthase activity.