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A more recent version of this article appeared on November 1, 2007 Originally published as MBC in Press, 10.1091/mbc.E07-05-0457 on September 5, 2007
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Submitted on May 16, 2007
Revised on August 20, 2007
Accepted on August 28, 2007
Institute of Plant Sciences, Eidgenössiche Technische Hochschule Zurich, 8092 Zurich, Switzerland
Monitoring Editor: Suresh Subramani
Inorganic polyphosphate (poly P) is a biopolymer that occurs in all organisms and cells and in many cellular compartments. It is involved in numerous biological phenomena and functions in cellular processes in all organisms. However, even the most fundamental aspects of poly P metabolism are largely unknown. In yeast, large amounts of poly P accumulate in the vacuole during growth. It is neither known how this poly P pool is synthesized nor how it is remobilized from the vacuole to replenish the cytosolic phosphate pool. Here, we report a systematic analysis of the yeast phosphate transporters and their function in poly P metabolism. By using poly P content as a read-out, it was possible to define novel functions of the five phosphate transporters Pho84, Pho87, Pho89, Pho90 and Pho91, in budding yeast. Most notably, it was found that the low-affinity transporter Pho91 limits poly P accumulation in a strain lacking PHO85. This phenotype was not caused by a regulatory effect on the PHO pathway, but can be attributed to the unexpected localization of Pho91 in the vacuolar membrane. This finding is consistent with the hypothesis that Pho91 serves as a vacuolar phosphate transporter that exports phosphate from the vacuolar lumen to the cytosol.