ISOLATION AND CHARACTERIZATION OF YEAST MUTANTS BLOCKED IN MEVALONIC ACID FORMATION

Yeast mutants defective in .beta.-hydroxy-.beta.-methylglutaryl-CoA synthase and acetoacetyl-CoA thiolase were isolated. Mutants impaired in acetoacetyl-CoA thiolase range into 2 linked complementation units, erg 10 A and erg 10 B. Mutants deficient in .beta.-hydroxy-.beta.-methylglutaryl-CoA synthase belong to 2 unlinked complementation groups, erg 11 and erg 13. In strictly anaerobic growth conditions, mutants impaired in .beta.-hydroxy-.beta.-methylglutaryl-CoA synthase require mevalonic acid in addition to sterol and oleic acid, pointing out the role of mevalonic acid in other physiological functions than ergosterol precursor. Growth of mutants impaired in acetoacetyl-CoA thiolase cannot be recovered by mevalonic acid supplementation, suggesting a role of acetoacetyl-CoA or thiolase not linked to sterol pathway.