A MUTATION IN THE ZN-FINGER OF THE GAL4 HOMOLOG LAC9 RESULTS IN GLUCOSE REPRESSION OF ITS TARGET GENES

The transcriptional activator LAC9, a GAL4 homolog of Kluyveromyces lactis which mediates lactose and galactose-dependent activation of genes involved in the utilization of these sugars can also confer glucose repression to those genes. Here we report on the isolation and characterization of LAC9-2, an allele which encodes a glucose-sensitive activator in contrast to the one previously cloned. A single amino acid exchange of leu-104 to tryptophan is responsible for the glucose-insensitive phenotype. The mutation is located within the Zn-finger-like DNA binding domain which is highly conserved between LAC9 and GAL4. Glucose repression is also eliminated by duplication of the LAC9-2 alleie. The data indicate that LAC9 is a limiting factor for β-galactosidase gene expression under all growth conditions and that glucose reduces the activity of the activator. © 1990 Oxford University Press.