POLYPRENYL DIPHOSPHATE SYNTHASE ESSENTIALLY DEFINES THE LENGTH OF THESIDE-CHAIN OF UBIQUINONE

Ubiquinone, known as a component of the electron transfer system in ma ny organisms, has a different length of the isoprenoid side chain depe nding on the species, e.g., Escherichia coli, Saccharomyces cerevisiae and humans have 8, 6, and 10 isoprene units in the side chain, respec tively. No direct evidence has yet shown what factors define the lengt h of the side chain of ubiquinone. Here we proved that the polyprenyl diphosphate that was available in cells determined the length of the s ide chain of ubiquinone. E. coli octaprenyl diphosphate synthase (IspB ) was expressed with the mitochondrial import signal in S. cerevisiae. Such cells produced ubiquinone-8 in addition to the originally existi ng ubiquinone-6. When IspB was expressed in a S. cerevisiae COQ1 defec tive strain, IspB complemented the defect of the growth on the non-fer mentable carbon source. Those cells had the activity of octaprenyl dip hosphate synthase and produced only ubiquinone-8. These results opened the possibility of producing the type of ubiquinone that we need in S . cerevisiae simply by expressing the corresponding polyprenyl diphosp hate synthase.