CLONING OF THE SDSA GENE ENCODING SOLANESYL DIPHOSPHATE SYNTHASE FROMRHODOBACTER-CAPSULATUS AND ITS FUNCTIONAL EXPRESSION IN ESCHERICHIA-COLI AND SACCHAROMYCES-CEREVISIAE

Different organisms produce different species of isoprenoid quinones, each with ifs own distinctive length, These differences in length are commonly exploited in microbial classification, The side chain length of quinone is determined by the nature of the polyprenyl diphosphate s ynthase that catalyzes the reaction, To determine if the side chain le ngth of ubiquinone (UQ) has any distinct role to play in the metabolis m of the cells in which it is found, we cloned the solanesyl diphospha te synthase gene (sdsA) from Rhodobacter capsulatus SB1003 and express ed it in Escherichia coli and Saccharomyces cerevisiae. Sequence analy sis revealed that the sdsA gene encodes a 325-amino-acid protein which has similarity (27 to 40%) with other prenyl diphosphate synthases. E xpression of the sdsA gene complemented a defect in the octaprenyl dip hosphate synthase gene of E. coli and the nonrespiratory phenotype res ulting from a defect in the hexaprenyl diphosphate synthase gene of S. cerevisiae. Both E. coli and S. cerevisiae expressing the sdsA gene m ainly produced solanesyl diphosphate, which resulted in the synthesis of UQ-9 without any noticeable effect on the growth of tile cells, Thu s, it appears that UQ-9 can replace the function of UQ-8 in E. coli an d UQ-6 in S. cerevisiae. Taken together with previous results, the res ults described here imply that the side chain length of UQ is not a cr itical factor for the survival of microorganisms.