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 m evalonate diphosphate to isopentenyl diphosphate, the building block o f isoprenoids. We used the Saccharomyces cerevisiae temperature-sensit ive mutant defective for mevalonate diphosphate decarboxylase previous ly described (C. Chambon, V. Ladeveve, M. Servouse, L. Blanchard, C. J avelot, B. Vladescu, and F. Karst, Lipids 26:633-636, 1991) to charact erize the mutated allele, We showed that a single change in a conserve d amino acid accounts for the temperature-sensitive phenotype of the m utant, Complementation experiments were done both in the erg19-mutated background and in a strain in which the ERG19 gene, which was shown t o be an essential gene for yeast, was disrupted, Epitope tagging of th e wild-type mevalonate diphosphate decarboxylase allowed us to isolate the enzyme in an active form by a versatile one-step immunoprecipitat ion procedure, Furthermore, during the course of this study, we observ ed 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-ty pe strain, suggesting that this enzyme may be a key enzyme in mevalona te pathway regulation.