title: Gal80 dimerization and the yeast GAL gene switch.
abstract: The Saccharomyces cerevisiae Gal80 protein has two binding partners: Gal4 and Gal3. In the absence of galactose, Gal80 binds to and inhibits the transcriptional activation domain (AD) of the GAL gene activator, Gal4, preventing GAL gene expression. Galactose triggers an association between Gal3 and Gal80, relieving Gal80 inhibition of Gal4. We selected for GAL80 mutants with impaired capacity of Gal80 to bind to Gal3 or Gal4AD. Most Gal80 variants selected for impaired binding to Gal4AD retained their capacity to bind to Gal3 and to self-associate, whereas most of those selected for impaired binding to Gal3 lost their ability to bind to Gal4AD and self-associate. Thus, some Gal80 amino acids are determinants for both the Gal80-Gal3 association and the Gal80 self-association, and Gal80 self-association may be required for binding to Gal4AD. We propose that the binding of Gal3 to the Gal80 monomer competes with Gal80 self-association, reducing the amount of the Gal80 dimer available for inhibition of Gal4.
authors.affiliation: Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, Hershey, 17033, USA.
authors.forename: Vepkhia
authors.initials: V
authors.lastname: Pilauri
authors.forename: Maria
authors.initials: M
authors.lastname: Bewley
authors.forename: Cuong
authors.initials: C
authors.lastname: Diep
authors.forename: James
authors.initials: J
authors.lastname: Hopper
mesh_terms: D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins; D019281:Dimerization; D005656:Fungal Proteins / Q000737:chemistry*; D005690:Galactose / Q000737:chemistry / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D008954:Models, Biological; D008957:Models, Genetic; D008958:Models, Molecular; D016296:Mutagenesis; D009154:Mutation; D020125:Mutation, Missense; D009841:Oligonucleotides / Q000235:genetics; D010641:Phenotype; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry*; D014157:Transcription Factors / Q000737:chemistry; D014158:Transcription, Genetic; D020798:Two-Hybrid System Techniques
chemical_list: D017931:DNA Primers; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; C055002:GAL80 protein, S cerevisiae; C099289:Gal3 protein, S cerevisiae; D009841:Oligonucleotides; D020033:Protein Isoforms; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D005690:Galactose