Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Ogawa, Nobuo
Mailing Address: Department of Biochemistry, Stanford University, Beckman Center B451, Stanford, CA 94305-5307, USA
Email Address: nogawa@cmgm.stanford.edu
Phone & FAX numbers: 1-650-723-5995 & 1-650-725-6044

#011

A set of PHO-regulated genes identified by DNA microarrays are involved in metabolism of inorganic polyphosphate, which functions as a P i reservoir and a metal chelator.
Nobuo Ogawa (1), Joseph DeRisi (2), Patrick O. Brown (1)
(1) Department of Biochemistry, Stanford University, Beckman Center B451, Stanford, CA 94305-5307, USA; (2) Department of Biochemistry and Biophysics, UCSF, 513 Parnassus Ave, San Francisco, CA 94143

When grown in media limited for inorganic phosphate (Pi), several genes regulated by the PHO system are transcriptionally induced in S. cerevisiae. Using DNA microarrays, we identified at least twenty of the PHO-regulated genes including eight previously uncharacterized genes named PHM1 to 8 (phosphate metabolism). Phm1, 2, 3 and 4 share homology with each other. Strains with disruptions in either phm3, phm4, or phm1 phm2 double deletions, had no detectable levels of inorganic polyphosphate (polyP) which normally accumulates in large amounts in the vacuole. Phm2-GFP was localized in vacuoles. It is known that several v-ATPase mutants fail to accumulate detectable levels of polyP, but this deficiency could be partially suppressed by a low pH medium, indicating that the involvement of v-ATPase in polyP synthesis are indirect. In contrast, low pH could not surppress the similar deficiency in the phm mutants. So far, Phm1, 2, 3 and 4 are the closest candidates for the polyP-synthesis enzyme which has not yet been identified in eukaryotes. In addition, PHM5 is supposed to encode an endopolyphosphatase in vacuoles. PolyP is thought to act as a reservoir of Pi and a chelator of metal ions. The polyP-deficient phm mutants showed lower final cell densities than their parental strain in Pi-free media. These mutants also grew significantly slower on the media containing 200 mM CaCl2 or 5 mM ZnCl2. Thus, polyP synthesis and degradation are an important part of Pi metabolism in yeast.

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