Assembly of polyisoprenoid side chains. The polyprenyl synthase of coenzyme Q biosynthesis catalyzes the formation from isopentenyl diphosphate of all trans-polyprenyl pyrophosphates generally ranging in length of between 6 and 10 isoprene units depending on the species. Binds 2 Mg(2+) ions per subunit. Cofactor biosynthesis; ubiquinone biosynthesis. Present with 1560 molecules/cell in log phase SD medium. Belongs to the FPP/GGPP synthase family.