Molecular and General Genetics MGG

, Volume 258, Issue 6, pp 628–638

Identification, cloning and characterization of a derepressible Na+-coupled phosphate transporter in Saccharomyces cerevisiae

  • P. Martinez
  • B. L. Persson
ORIGINAL PAPER

DOI: 10.1007/s004380050776

Cite this article as:
Martinez, P. & Persson, B. Mol Gen Genet (1998) 258: 628. doi:10.1007/s004380050776

Abstract

Based on the high sequence homology between the yeast ORF YBR296c (accession number P38361 in the SWISS-PROT database) and the PHO4 gene of Neurospora crassa, which codes for a Na+/Pi cotransporter with twelve putative transmembrane domains, the YBR296c ORF was considered to be a promising candidate gene for a plasma membrane-bound phosphate transporter in Saccharomyces cerevisiae. Therefore, this gene, here designated PHO89, was cloned and a set of deletion mutants was constructed. We then studied their Pi uptake activity under different conditions. We show here that a transport activity displayed by PHO89 strains under alkaline conditions and in the presence of Na+ is absent in pho89 null mutants. Moreover, when the pH was lowered to pH 4.5 or when Na+ was omitted, this activity decreased significantly, reaching values close to those exhibited by the Δpho89 mutant. Studies of the acid phosphatase activity of these strains, as well as promoter sequence analysis, suggest that expression of the PHO89 gene is under the control of the PHO regulatory system. Northern analysis shows that this gene is only transcribed under conditions of Pi limitation. This is, to our knowledge, the first demonstration that the PHO89 gene codes for the Na+/Pi cotransporter previously characterized by kinetic studies, and represents the only Na+-coupled secondary anion transport system so far identified in S. cerevisiae. Pho89p has been shown to have an apparent Km of 0.5 μM and a pH optimum of 9.5, and is highly specific for Na+; activation of transport is maximal at a Na+ concentration of 25 mM.

Key words Phosphate transportPHO89Saccharomyces cerevisiae

Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • P. Martinez
    • 1
  • B. L. Persson
    • 1
  1. 1.Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden Fax: +46-8-15 3679; e-mail: Bengt_P@biokemi.su.seSE
  2. 2.Department of Engineering and Natural Sciences, Växjö University, S-351 95 Växjö, SwedenSE