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EMBO Rep. 2009 Sep;10(9):1003-8. doi: 10.1038/embor.2009.105. Epub 2009 Jul 10.

The SPX domain of the yeast low-affinity phosphate transporter Pho90 regulates transport activity.

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  • 1Institute of Plant Sciences, ETH Zurich, Universitätstrasse 2, 8092 Zurich, Switzerland.


Yeast has two phosphate-uptake systems that complement each other: the high-affinity transporters (Pho84 and Pho89) are active under phosphate starvation, whereas Pho87 and Pho90 are low-affinity transporters that function when phosphate is abundant. Here, we report new regulatory functions of the amino-terminal SPX domain of Pho87 and Pho90. By studying truncated versions of Pho87 and Pho90, we show that the SPX domain limits the phosphate-uptake velocity, suppresses phosphate efflux and affects the regulation of the phosphate signal transduction pathway. Furthermore, split-ubiquitin assays and co-immunoprecipitation suggest that the SPX domain of both Pho90 and Pho87 interacts physically with the regulatory protein Spl2. This work suggests that the SPX domain inhibits low-affinity phosphate transport through a physical interaction with Spl2.

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