Polyprenol formation in the yeast Saccharomyces cerevisiae: effect of farnesyl diphosphate synthase overexpression.

Biosynthesis of polyprenols was followed in the erg mutants of Saccharomyces cerevisiae impaired in various steps of the mevalonate pathway. The end products of the enzymatic reaction carried out in vitro, in the wild type yeast and all mutants tested, were identified as dehydrodolichols (alpha-unsaturated polyprenols) whereas in vivo, yeast synthesize dolichols (alpha-saturated polyprenols) (Biochimie, 1996.78:111-112.) The strain defective in the farnesyl diphosphate (FPP) synthase, (coded by the erg20-2 gene) required the presence of exogenous FPP for synthesis of dehydrodolichols to occur in vitro. Overexpression of the ERG20 gene restored synthesis of polyprenols in vitro indicating that FPP is the allylic "starter" for cis-prenyltransferase in yeast. Overexpression of the ERG20 gene in the erg 9 mutant, defective in squalene synthase activity, not only restored synthesis of dehydrodolichols in vitro, but also increased the synthesis of dolichols in vivo, almost 10-fold in comparison with wild type yeast. On the other hand overexpression of the mutated FPP synthase, coded by the gene erg20-2 in the same genetic background, resulted in a 100-fold increase of the amount of dehydrodolichols. Interestingly, in addition to the family of typical for yeast C60-C80 compounds, dehydrodolichols of chain length up to C135 were synthesized both in vitro and in vivo.