A single amino-acid substitution in the yeast mevalonate diphosphate decarboxylase leads to a defect in the homodimerization of the protein

The functional yeast ERG19 allele encoding mevalonate diphosphate decarboxy lase (MVD) and the mutated recessive allele erg19 leading to a decrease of sterol production and a thermosensitive phenotype, were cloned and characte rized. The mutated erg19 allele bears a single amino acid leu79-to-pro subs titution. This mutation doesn't affect the level of production of the mutat ed enzyme. Two-hybrid assays showed that the yeast MVD forms homodimers; th e single point mutation was shown to impair the dimerization of the mutated enzyme, leading to a less active MVD.