Gene activation by dissociation of an inhibitor from a transcriptional activation domain.
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.
Jiang
Fenglei
F
Department of Biochemistry, the Ohio State University, 484 West 12th Avenue, Columbus, OH 43210, USA.
Frey
Benjamin R
BR
Evans
Margery L
ML
Friel
Jordan C
JC
Hopper
James E
JE
D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D005686:Galactokinase / Q000187:drug effects / Q000378:metabolism*; D005690:Galactose / Q000494:pharmacology; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D012097:Repressor Proteins / Q000187:drug effects / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000187:drug effects / Q000378:metabolism*; D014157:Transcription Factors / Q000187:drug effects / Q000378:metabolism*; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; C052130:GAL4 protein, S cerevisiae; C055002:GAL80 protein, S cerevisiae; C099289:Gal3 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C524219:GAL1 protein, S cerevisiae; D005686:Galactokinase; D005690:Galactose