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. Supplies nona and decaprenyl diphosphate, the precursors for the side chain of the isoprenoid quinones ubiquinone-9 (Q9) and ubiquinone-10 (Q10) respectively. The enzyme adds isopentenyl diphosphate molecules sequentially to farnesyl diphosphate with trans stereochemistry (By similarity). May play a role during cerebellar development (By similarity). May regulate mitochondrial respiratory chain function (By similarity). (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 Cofactor biosynthesis; ubiquinone biosynthesis. Heterotetramer composed of 2 PDSS1/DPS1 and 2 PDSS2/DLP1 subunits. Belongs to the FPP/GGPP synthase family.