Catalyzes the sequential condensation of isopentenyl diphosphate (IPP) in the cis configuration with (2Z,6E)-farnesyl diphosphate (Z-FPP or EZ-FPP) generating the 50 carbon product trans,polycis-decaprenyl diphosphate. When (2E,6E)-farnesyl diphosphate (E-FPP or EE-FPP) is used in vitro, both primary products decaprenyl diphosphate and (2E,6E,10E)-geranylgeranyl diphosphate (EEE-GGPP) are synthesized. M.tuberculosis does not synthesize (2E,6E,10Z)-geranylgeranyl diphosphate (EEZ-GGPP) and heptaprenyl diphosphate. Can also accept many different allylic substrates, including E-geranyl diphosphate (E-GPP), neryl diphosphate (NPP), and all-trans-geranyl-geranyl diphosphate. (2Z,6E)-farnesyl diphosphate + 7 isopentenyl diphosphate = (2Z,6Z,10Z,14Z,18Z,22Z,26Z,30Z,34E)-decaprenyl diphosphate + 7 diphosphate (2E,6E)-farnesyl diphosphate + n isopentenyl diphosphate = di-trans,poly-cis-polyprenyl diphosphate + n diphosphate Binds 2 magnesium ions per subunit. Can also use manganese as divalent cation, however calcium and zinc ions are much less effective. Activated by dithiothreitol and inhibited by EDTA. Optimum pH is between 7.5 and 8.5. Homodimer. Belongs to the UPP synthase family.