Heterotetrameric enzyme that catalyzes the condensation of farnesyl diphosphate (FPP), which acts as a primer, and isopentenyl diphosphate (IPP) to produce prenyl diphosphates of varying chain lengths and participates in the determination of the side chain of ubiquinone (PubMed:16262699). Supplies nona and decaprenyl diphosphate, the precursors for the side chain of the isoprenoid quinones ubiquinone-9 (Q9)and ubiquinone-10 (Q10) respectively (PubMed:16262699). The enzyme adds isopentenyl diphosphate molecules sequentially to farnesyl diphosphate with trans stereochemistry (PubMed:16262699). (2E,6E)-farnesyl diphosphate + 7 isopentenyl diphosphate = all-trans-decaprenyl diphosphate + 7 diphosphate (2E,6E)-farnesyl diphosphate + 6 isopentenyl diphosphate = all-trans-nonaprenyl diphosphate + 6 diphosphate Binds 2 Mg(2+) ions per subunit. Cofactor biosynthesis; ubiquinone biosynthesis. Heterotetramer composed of 2 PDSS1/DPS1 and 2 PDSS2/DLP1 subunits. The disease is caused by variants affecting the gene represented in this entry. Belongs to the FPP/GGPP synthase family.