Relationships between trehalose metabolism and maltose utilization in Saccharomyces cerevisiae : II. Effect of Constitutive MAL Genes.

A pattern of active accumulation of trehalose during growth on glucose medium, TAC(+) phenotype, is controlled by a polymeric series of maltose fermentation (MAL) genes. An essential requirement for expression of the TAC(+) phenotype is that the MAL gene be in the constitutive state, MAL (c). Mutation of a constitutive MAL allele to a maltose- inducible or nonfermenting (mal) state, alters the pattern of trehalose metabolism so that little or no trehalose accumulation occurs during growth on glucose medium. The TAC(+) phenotype is obtained in MAL (c) strains whether or not α-glucosidase formation is sensitive or resistant to carbon catabolite repression. However, trehalose accumulation is sensitive to glucose levels even in MAL (c) strains in which α-glucosidase formation is insensitive to catabolite repression. The effects of constitutive MAL genes on trehalose accumulation cannot be accounted for by an increase in trehalose-6 phosphate synthase or a decrease in trehalase as determined in vitro. A mechanism is proposed in which the gene-product of a MAL gene serves as a common positive regulator for expression of four genes coding respectively for maltose permease, maltase, α-methylglucosidase and a component of the trehalose accumulation system.