Gene activation by dissociation of an inhibitor from a transcriptional activation domain

Mol Cell Biol. 2009 Oct;29(20):5604-10. doi: 10.1128/MCB.00632-09. Epub 2009 Aug 3.


Gal4 is a prototypical eukaryotic transcriptional activator whose recruitment function is inhibited in the absence of galactose by the Gal80 protein through masking of its transcriptional activation domain (AD). A long-standing nondissociation model posits that galactose-activated Gal3 interacts with Gal4-bound Gal80 at the promoter, yielding a tripartite Gal3-Gal80-Gal4 complex with altered Gal80-Gal4 conformation to enable Gal4 AD activity. Some recent data challenge this model, whereas other recent data support the model. To address this controversy, we imaged fluorescent-protein-tagged Gal80, Gal4, and Gal3 in live cells containing a novel GAL gene array. We find that Gal80 rapidly dissociates from Gal4 in response to galactose. Importantly, this dissociation is Gal3 dependent and concurrent with Gal4-activated GAL gene expression. When galactose-triggered dissociation is followed by galactose depletion, preexisting Gal80 reassociates with Gal4, indicating that sequestration of Gal80 by Gal3 contributes to the observed Gal80-Gal4 dissociation. Moreover, the ratio of nuclear Gal80 to cytoplasmic Gal80 decreases in response to Gal80-Gal3 interaction. Taken together, these and other results provide strong support for a GAL gene switch model wherein Gal80 rapidly dissociates from Gal4 through a mechanism that involves sequestration of Gal80 by galactose-activated Gal3.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • DNA-Binding Proteins / drug effects
  • DNA-Binding Proteins / metabolism*
  • Galactokinase / drug effects
  • Galactokinase / metabolism*
  • Galactose / pharmacology
  • Gene Expression Regulation, Fungal / drug effects
  • Gene Expression Regulation, Fungal / genetics
  • Gene Expression Regulation, Fungal / physiology
  • Promoter Regions, Genetic / drug effects
  • Promoter Regions, Genetic / physiology
  • Repressor Proteins / drug effects
  • Repressor Proteins / metabolism*
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae Proteins / drug effects
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Transcription Factors / drug effects
  • Transcription Factors / metabolism*
  • Transcriptional Activation*


  • DNA-Binding Proteins
  • GAL4 protein, S cerevisiae
  • GAL80 protein, S cerevisiae
  • Gal3 protein, S cerevisiae
  • Repressor Proteins
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • GAL1 protein, S cerevisiae
  • Galactokinase
  • Galactose