Effects of methylphosphonate, a phosphate analogue, on the expression and degradation of the high-affinity phosphate transporter Pho84, in Saccharomyces cerevisiae.
In Saccharomyces cerevisiae, the Pho84 high-affinity transport system is the major phosphate transporter activated when the cells experience a limitation in external phosphate. In this study, we have compared the phosphate-responsive mechanism of cells expressing PHO84 with a Deltapho84 strain by use of a phosphate analogue, methylphosphonate, which was judged to be suitable for assessment of phosphate homeostasis in the cells. Intracellular levels of the analogue, which in several respects mimicks phosphate, were monitored by (31)P NMR spectroscopy. Results show that methylphosphonate is a nonhydrolyzable and nonutilizable analogue that cannot be used to replenish phosphate or polyphosphate in yeast cells grown under conditions of phosphate limitation. However, the presence of methylphosphonate under such conditions represses the Pho5 acidic phosphatase activity of PHO84 cells, a finding that implies a direct role of the analogue in the regulation of phosphate-responsive genes and/or proteins. Likewise, accumulation of the Pho84 protein at the plasma membrane of the same cells is inhibited by methylphosphonate, although the derepressive expression of the PHO84 gene is unperturbed. Thus, a post-transcriptional regulation is suggested. Supportive of this suggestion is the fact that addition of methylphosphonate to cells with abundant and active Pho84 at the plasma membrane causes enhanced internalization of the Pho84 protein. Altogether, these observations suggest that the Pho84 transporter is regulated not only at the transcriptional level but also by a direct molecule-sensing mechanism at the protein level.
Pratt
James R
JR
Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, S-106 91 Stockholm, Sweden.
Mouillon
Jean-Marie
JM
Lagerstedt
Jens O
JO
Pattison-Granberg
Johanna
J
Lundh
Kent I
KI
Persson
Bengt L
BL
D000135:Acid Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D016259:Genes, myc; D006863:Hydrogen-Ion Concentration; D009943:Organophosphorus Compounds / Q000737:chemistry* / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*; D028081:Proton-Phosphate Symporters / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D013489:Suppression, Genetic
D009943:Organophosphorus Compounds; C105495:PHO84 protein, S cerevisiae; D010710:Phosphates; D028081:Proton-Phosphate Symporters; D029701:Saccharomyces cerevisiae Proteins; C032627:methylphosphonic acid; D000135:Acid Phosphatase