Schizosaccharomyces pombe produces ubiquinone-10 whose side chain is thought to be provided by the product generated by decaprenyl diphosphate synthase. To understand the mechanism of ubiquinone biosynthesis in S. pombe, we have cloned the gene encoding decaprenyl diphosphate synthase by the combination of PCR amplification of the fragment and subsequent library screening. The determined DNA sequence of the cloned gene, called dps, revealed that the dps gene encodes a 378-amino-acid protein that has the typical conserved regions observed in many polyprenyl diphosphate synthases. Computer-assisted homology search indicated that Dps is 45 and 33% identical with hexaprenyl diphosphate synthase from Saccharomyces cerevisiae and octaprenyl diphosphate synthase from Escherichia coli, respectively. An S. pombe dps-deficient strain was constructed. This disruptant was not able to synthesize ubiquinone and had no detectable decaprenyl diphosphate synthase activity, indicating that the dps gene is unique and responsible for ubiquinone biosynthesis. The S. pombe dps-deficient strain could not grow on either rich medium supplemented with glycerol or on minimal medium supplemented with glucose. The dps-deficient strain required cysteine or glutathione for full growth on the minimal medium. In addition, the dps-deficient strain is more sensitive to H2O2 and Cu2+ than the wild type. These results suggests a role of ubiquinone as an antioxidant in fission yeast cells.