Regulation of maltose fermentation in Saccharomyces carlsbergensis

Summary

0405 02

• 1) In addition to the mutant C2, described previously, 9 other constitutive MLA ₆-mutants have been isolated. These, like C2, are sensitive to catabolite repression and not super-inducible by maltose. One of these mutants (C19) is dominant relative to the wild type strain and to mal ₆-mutants. The others, like C2, are recessive to the wild type, and their hybrids with mal ₆-mutants show a partial or complete loss of the constitutivity and a partial or complete restoration of the inducibility, depending on the particular mutant combination used, which indicates that these recessive constitutive MAL ₆-mutations are allelic to the mal ₆-mutations. The mutation MAL ^c19 ₆ is possiblynot allelic to the mal ₆-mutations.

• 2) A maltose negative mutation (mal _x ) of a type different from the mal ₆-mutations was isolated. This mutation, unlinked to MAL ₆, is not expressed in combination with the wild type MAL ₆-gene, but only in the presence of constitutive MAL ^c ₆ -alleles by changing the constitutive phenotype (not the genotype) into a mal ₆-phenotype. Similarly, another mutation (mal _y ) was found that is linked neither to MAL ₆ nor to mal _x and that changes the phenotype of the constitutive allele MAL ^c14 ₆ into a mal ₆-phenotype. In contrast with mal _x , mutation mal _y is specific for the allele MAL ^c14 ₆ .

• 3) The properties of the new constitutive mutants and the nature of the suppressors mal _x and mal _y and their importance for mapping constitutive MAL ^c ₆ -alleles are discussed.