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The transcription factor, the Cdk, its cyclin and their regulator: directing the transcriptional response to a
K Hirst1, F Fisher, P C McAndrew
1Eukaryotic Transcription Laboratory, Marie Curie Research Institute, Oxted, Surrey, UK.
Abstract:
The Pho80-Pho85 cyclin-cdk complex prevents transcription of PHO5 by inhibiting the ability of the basic-helix-loop-helix transcription factor Pho4 to activate transcription in response to high phosphate conditions. In low phosphate the Pho80-Pho85 complex is inactivated and Pho4 is then able to activate the acid phosphatase gene PHO5. We show here that Pho4 and the homeobox protein Pho2 interact in vivo and act cooperatively to activate the PHO5 UAS, with interaction being regulated by the phosphate switch. In addition, we also demonstrate that an additional factor, Pho81, interacts in high phosphate with both the Pho80 cyclin and with Pho4. In low phosphate, Pho80 and Pho81 dissociate from Pho4, but retain the ability to interact with each other. The evidence presented here supports the idea that Pho81 acts as a phosphate-sensitive trigger that regulates the ability of the Pho80-Pho85 cyclin-cdk complex to bind Pho4, while DNA binding by Pho4 is dependent on the phosphate-sensitive interaction with Pho2.
Insights
The Pho80-Pho85 complex regulates PHO5 gene transcription by controlling Pho4 activity. Phosphate levels dictate interactions between Pho4, Pho2, and Pho81, enabling gene activation in low phosphate conditions.
Area of Science:
- * Molecular Biology
- * Gene Regulation
- * Yeast Genetics
Background:
- * The PHO5 gene encodes acid phosphatase, crucial for phosphate metabolism in yeast.
- * Transcription of PHO5 is tightly regulated by phosphate availability.
- * The Pho80-Pho85 cyclin-cdk complex inhibits Pho4, a key transcription factor, under high phosphate conditions.
Purpose of the Study:
- * To elucidate the molecular mechanisms governing PHO5 gene transcription.
- * To investigate the roles of Pho2 and Pho81 in regulating Pho4 activity.
- * To understand how the phosphate switch controls the interaction network.
Main Methods:
- * In vivo interaction studies (e.g., yeast two-hybrid, co-immunoprecipitation).
- * Analysis of gene activation under varying phosphate conditions.
- * Protein-DNA binding assays.
Main Results:
- * Pho4 and Pho2 interact in vivo and cooperatively activate the PHO5 upstream activating sequence (UAS).
- * This Pho4-Pho2 interaction is regulated by the phosphate-dependent switch.
- * Pho81 interacts with Pho80 and Pho4 in high phosphate; these interactions dissociate in low phosphate.
Conclusions:
- * Pho81 acts as a phosphate-sensitive regulator, modulating Pho80-Pho85 complex binding to Pho4.
- * Pho4 DNA binding is dependent on its phosphate-sensitive interaction with Pho2.
- * This intricate regulatory network ensures precise control of PHO5 expression.