A process for microbiologically producing coenzyme Q10 at a high efficiency by using a gene of the synthesis of coenzyme Q10 side chain originating in a fungus belonging to the genus <i>Saitoella.</i> A DNA having the base sequence represented by SEQ ID NO:1; a DNA having a base sequence derived from the base sequence represented by SEQ ID NO:1 by deletion, addition, insertion and/or substitution of one or more bases and encoding a protein having a decaprenyl diphosphate synthase activity; and a DNA being hybridizable under stringent conditions with the DNA comprising the base sequence represented by SEQ ID NO:1 and encoding a protein having a decaprenyl diphosphate synthase activity.
