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	Biochem. Biophys. Res. Commun. Jan (2008); 365(4):821-5
Ddi1p and Rad23p play a cooperative role as negative regulators in the PHO pathway in Saccharomyces cerevisiae-
Auesukaree C, Fuchigami I, Homma T, Kaneko Y, Harashima S
Department of Biology, Faculty of Science, Mahidol University, Rama VI Road, Bangkok 10400, Thailand-
Abstract: In Saccharomyces cerevisiae, the PHO pathway regulates expression of phosphate-responsive genes such as PHO5, which encodes repressible acid phosphatase -rAPase-- In this pathway, Pho81p functions as an inhibitor of the cyclin-cyclin-dependent kinase -CDK- complex Pho80p-Pho85p- However, the mechanism regulating the inhibitory activity of Pho81p is poorly understood- Through use of the yeast two-hybrid system, we identified the UbL-UbA protein Ddi1p as a Pho81p-binding protein- Further, Pho81p levels were found to be low under high-phosphate condition and high during phosphate starvation, indicating that Pho81p is regulated by phosphate concentration- However, our results revealed that Ddi1p and its associated protein Rad23p are not involved in the decrease in Pho81p level under high-phosphate condition- Significantly, the Deltaddi1Deltarad23 strain exhibited a remarkable increase in rAPase activity at an intermediate-phosphate concentration of 0-4mM, suggesting that Ddi1p and Rad23p play a cooperative role as negative regulators in the PHO pathway-
[PUBMED: 18035052]