Interaction of super-repressible and dominant constitutive mutations for the synthesis of galactose pathway enzymes in Saccharomyces cerevisiae

Summary Two dominant uninducible mutant alleles in the gal80 locus were identified. The GAL80 ^s-1 and GAL80 ^s-2 mutants showed novel phenotypes in response to the newly isolated GAL81-1 mutant allele, a dominant constitutive mutation linked to the gal4 locus; the GAL80 ^s-1 GAL81-1 strain was inducible and the GAL80 ^s-2 GAL81-1 strain was uninducible. Many galactose positive revertants from the GAL80 ^s-2 GAL81-1 strain were isolated. It was proved that each revertant was due to a secondary mutation either in the gal80 or GAL81 locus, whereas revertants due to mutation at the supposed controlling site for the structural gene cluster of the galactose-pathway enzymes have not been isolated.This study was supported in part by grant no. 048164 to Y. Oshima from the Scientific Research Fund of the Ministry of Eduction, Japan