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Partially phosphorylated Pho4 activates transcription of a subset of phosphate-responsive genes.

Springer M, Wykoff DD, Miller N, O'Shea EK - PLoS Biol. (2003)

Bottom Line: This Pho4 phosphoform binds differentially to phosphate-responsive promoters and helps to trigger differential gene expression.Our results demonstrate that three transcriptional outputs can be generated by a pathway whose regulation is controlled by one kinase, Pho80-Pho85, and one transcription factor, Pho4.Differential phosphorylation of Pho4 by Pho80-Pho85 produces phosphorylated forms of Pho4 that differ in their ability to activate transcription, contributing to multiple outputs.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of California, San Francisco, USA.

ABSTRACT
A cell's ability to generate different responses to different levels of stimulus is an important component of an adaptive environmental response. Transcriptional responses are frequently controlled by transcription factors regulated by phosphorylation. We demonstrate that differential phosphorylation of the budding yeast transcription factor Pho4 contributes to differential gene expression. When yeast cells are grown in high-phosphate growth medium, Pho4 is phosphorylated on four critical residues by the cyclin-CDK complex Pho80-Pho85 and is inactivated. When yeast cells are starved for phosphate, Pho4 is dephosphorylated and fully active. In intermediate-phosphate conditions, a form of Pho4 preferentially phosphorylated on one of the four sites accumulates and activates transcription of a subset of phosphate-responsive genes. This Pho4 phosphoform binds differentially to phosphate-responsive promoters and helps to trigger differential gene expression. Our results demonstrate that three transcriptional outputs can be generated by a pathway whose regulation is controlled by one kinase, Pho80-Pho85, and one transcription factor, Pho4. Differential phosphorylation of Pho4 by Pho80-Pho85 produces phosphorylated forms of Pho4 that differ in their ability to activate transcription, contributing to multiple outputs.

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Models for Differential Gene Regulation(A) Differential affinity of Pho4 for the PHO84 and PHO5 promoters can cause differential gene expression. Simulated curves of the percent occupancy of Pho4 at the PHO84 and PHO5 promoters, assuming Michaelian binding. Pho4 was modeled as having a Kd of 10 at the PHO84 promoter and of 100 at the PHO5 promoter. Phosphorylation of Pho4 was simulated as raising the Kd of Pho4 to 40 at the PHO84 promoter and to 400 at the PHO5 promoter. The nuclear concentration of Pho4 was assumed to be 7.5-fold higher in intermediate-phosphate medium than in high-phosphate medium and 10-fold higher in no-phosphate medium than in high-phosphate medium.(B) Kinetic diagram of the steps leading to active transcription at the PHO84 and PHO5 promoters. Differences in the kinetic mechanisms of activation of PHO84 and PHO5 can lead to differential gene expression. Even if promoter occupancy is high at the PHO5 promoter, if the transcriptional activation step is slow compared to the rate of Pho4 phosphorylation and inactivation, PHO5 will not be induced.
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pbio.0000028-g006: Models for Differential Gene Regulation(A) Differential affinity of Pho4 for the PHO84 and PHO5 promoters can cause differential gene expression. Simulated curves of the percent occupancy of Pho4 at the PHO84 and PHO5 promoters, assuming Michaelian binding. Pho4 was modeled as having a Kd of 10 at the PHO84 promoter and of 100 at the PHO5 promoter. Phosphorylation of Pho4 was simulated as raising the Kd of Pho4 to 40 at the PHO84 promoter and to 400 at the PHO5 promoter. The nuclear concentration of Pho4 was assumed to be 7.5-fold higher in intermediate-phosphate medium than in high-phosphate medium and 10-fold higher in no-phosphate medium than in high-phosphate medium.(B) Kinetic diagram of the steps leading to active transcription at the PHO84 and PHO5 promoters. Differences in the kinetic mechanisms of activation of PHO84 and PHO5 can lead to differential gene expression. Even if promoter occupancy is high at the PHO5 promoter, if the transcriptional activation step is slow compared to the rate of Pho4 phosphorylation and inactivation, PHO5 will not be induced.

Mentions: We propose that differences in the regulation of PHO5 and PHO84 are caused by affinity differences and kinetic mechanisms. If the PHO84 promoter has higher affinity for Pho4 than does the PHO5 promoter, differential occupancy of these promoters in intermediate-phosphate conditions may lead to differences in transcription (Figure 6A). For example, the concentration of Pho4 and its affinity for DNA may be such that in no-phosphate conditions Pho4 binding at the PHO84 promoter is saturated, but binding at the PHO5 promoter is not. When Pho4 is phosphorylated on site 6, as in intermediate-phosphate conditions, we expect its affinity for DNA is reduced. This reduced affinity would have a more significant impact on the PHO5 promoter than on the PHO84 promoter because the PHO5 promoter was not saturated for binding. This differential occupancy could account for differences in transcription of these genes in intermediate-phosphate conditions.


Partially phosphorylated Pho4 activates transcription of a subset of phosphate-responsive genes.

Springer M, Wykoff DD, Miller N, O'Shea EK - PLoS Biol. (2003)

Models for Differential Gene Regulation(A) Differential affinity of Pho4 for the PHO84 and PHO5 promoters can cause differential gene expression. Simulated curves of the percent occupancy of Pho4 at the PHO84 and PHO5 promoters, assuming Michaelian binding. Pho4 was modeled as having a Kd of 10 at the PHO84 promoter and of 100 at the PHO5 promoter. Phosphorylation of Pho4 was simulated as raising the Kd of Pho4 to 40 at the PHO84 promoter and to 400 at the PHO5 promoter. The nuclear concentration of Pho4 was assumed to be 7.5-fold higher in intermediate-phosphate medium than in high-phosphate medium and 10-fold higher in no-phosphate medium than in high-phosphate medium.(B) Kinetic diagram of the steps leading to active transcription at the PHO84 and PHO5 promoters. Differences in the kinetic mechanisms of activation of PHO84 and PHO5 can lead to differential gene expression. Even if promoter occupancy is high at the PHO5 promoter, if the transcriptional activation step is slow compared to the rate of Pho4 phosphorylation and inactivation, PHO5 will not be induced.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC261874&req=5

pbio.0000028-g006: Models for Differential Gene Regulation(A) Differential affinity of Pho4 for the PHO84 and PHO5 promoters can cause differential gene expression. Simulated curves of the percent occupancy of Pho4 at the PHO84 and PHO5 promoters, assuming Michaelian binding. Pho4 was modeled as having a Kd of 10 at the PHO84 promoter and of 100 at the PHO5 promoter. Phosphorylation of Pho4 was simulated as raising the Kd of Pho4 to 40 at the PHO84 promoter and to 400 at the PHO5 promoter. The nuclear concentration of Pho4 was assumed to be 7.5-fold higher in intermediate-phosphate medium than in high-phosphate medium and 10-fold higher in no-phosphate medium than in high-phosphate medium.(B) Kinetic diagram of the steps leading to active transcription at the PHO84 and PHO5 promoters. Differences in the kinetic mechanisms of activation of PHO84 and PHO5 can lead to differential gene expression. Even if promoter occupancy is high at the PHO5 promoter, if the transcriptional activation step is slow compared to the rate of Pho4 phosphorylation and inactivation, PHO5 will not be induced.
Mentions: We propose that differences in the regulation of PHO5 and PHO84 are caused by affinity differences and kinetic mechanisms. If the PHO84 promoter has higher affinity for Pho4 than does the PHO5 promoter, differential occupancy of these promoters in intermediate-phosphate conditions may lead to differences in transcription (Figure 6A). For example, the concentration of Pho4 and its affinity for DNA may be such that in no-phosphate conditions Pho4 binding at the PHO84 promoter is saturated, but binding at the PHO5 promoter is not. When Pho4 is phosphorylated on site 6, as in intermediate-phosphate conditions, we expect its affinity for DNA is reduced. This reduced affinity would have a more significant impact on the PHO5 promoter than on the PHO84 promoter because the PHO5 promoter was not saturated for binding. This differential occupancy could account for differences in transcription of these genes in intermediate-phosphate conditions.

Bottom Line: This Pho4 phosphoform binds differentially to phosphate-responsive promoters and helps to trigger differential gene expression.Our results demonstrate that three transcriptional outputs can be generated by a pathway whose regulation is controlled by one kinase, Pho80-Pho85, and one transcription factor, Pho4.Differential phosphorylation of Pho4 by Pho80-Pho85 produces phosphorylated forms of Pho4 that differ in their ability to activate transcription, contributing to multiple outputs.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of California, San Francisco, USA.

ABSTRACT
A cell's ability to generate different responses to different levels of stimulus is an important component of an adaptive environmental response. Transcriptional responses are frequently controlled by transcription factors regulated by phosphorylation. We demonstrate that differential phosphorylation of the budding yeast transcription factor Pho4 contributes to differential gene expression. When yeast cells are grown in high-phosphate growth medium, Pho4 is phosphorylated on four critical residues by the cyclin-CDK complex Pho80-Pho85 and is inactivated. When yeast cells are starved for phosphate, Pho4 is dephosphorylated and fully active. In intermediate-phosphate conditions, a form of Pho4 preferentially phosphorylated on one of the four sites accumulates and activates transcription of a subset of phosphate-responsive genes. This Pho4 phosphoform binds differentially to phosphate-responsive promoters and helps to trigger differential gene expression. Our results demonstrate that three transcriptional outputs can be generated by a pathway whose regulation is controlled by one kinase, Pho80-Pho85, and one transcription factor, Pho4. Differential phosphorylation of Pho4 by Pho80-Pho85 produces phosphorylated forms of Pho4 that differ in their ability to activate transcription, contributing to multiple outputs.

Show MeSH