GENETIC AND BIOCHEMICAL-CHARACTERIZATION OF SACCHAROMYCES-CEREVISIAE MUTANTS RESISTANT TO TRIFLUOROLEUCINE

Eighteen mutants resistant to 5',5',5'-trifluoroleucine (TFL), a leuci ne analog, were isolated in Saccharomyces cerevisiae strains YNN281 an d YNN282. The mutants were characterized genetically and clustered in two groups, one comprising all the dominant (TFL1) and the other one a ll the recessive (tfl2) mutations. Genetic and biochemical data sugges ted that the dominant mutations are located on the LEU4 gene, coding f or alpha-isopropylmalate synthase I. These mutations resulted in accum ulation of leucine as a consequence of the synthesis of an enzyme inse nsitive to the feedback inhibition by leucine. Leucine excretion in th e TFL1 mutants appeared to be affected by the genetic background of th e strain and was greatly influenced by lysine metabolism. The measurem ent of intra-and extracellular amino acid concentrations in prototroph ic strains carrying TFL1 or tfl2 genes showed that both were leucine o verproducers. Some of the TFL-resistant mutants were tested in alcohol ic fermentation of grape must: analysis of the fermentation secondary metabolites showed that the major effect of the TFL-resistant strains was an increased production of isoamyl alcohol compared to that of the parental strain.