The Saccharomyces cerevisiae mevalonate diphosphate decarboxylase is essential for viability, and a single Leu-to-Pro mutation in a conserved sequence leads to thermosensitivity.

The mevalonate diphosphate decarboxylase is an enzyme which converts mevalonate diphosphate to isopentenyl diphosphate, the building block of isoprenoids. We used the Saccharomyces cerevisiae temperature-sensitive mutant defective for mevalonate diphosphate decarboxylase previously described (C. Chambon, V. Ladeveve, M. Servouse, L. Blanchard, C. Javelot, B. Vladescu, and F. Karst, Lipids 26:633-636, 1991) to characterize the mutated allele. We showed that a single change in a conserved amino acid accounts for the temperature-sensitive phenotype of the mutant. Complementation experiments were done both in the erg19-mutated background and in a strain in which the ERG19 gene, which was shown to be an essential gene for yeast, was disrupted. Epitope tagging of the wild-type mevalonate diphosphate decarboxylase allowed us to isolate the enzyme in an active form by a versatile one-step immunoprecipitation procedure. Furthermore, during the course of this study, we observed that a high level of expression of the wild-type ERG19 gene led to a lower sterol steady-state accumulation compared to that of a wild-type strain, suggesting that this enzyme may be a key enzyme in mevalonate pathway regulation.