title: Systematic screening of polyphosphate (poly P) levels in yeast mutant cells reveals strong interdependence with primary metabolism.
abstract: BACKGROUND
  Inorganic polyphosphate (poly P) occurs universally in all organisms from bacteria to man. It functions, for example, as a phosphate and energy store, and is involved in the activation and regulation of proteins. Despite its ubiquitous occurrence and important functions, it is unclear how poly P is synthesized or how poly P metabolism is regulated in higher eukaryotes. This work describes a systematic analysis of poly P levels in yeast knockout strains mutated in almost every non-essential gene.
  
  
  RESULTS
  After three consecutive screens, 255 genes (almost 4% of the yeast genome) were found to be involved in the maintenance of normal poly P content. Many of these genes encoded proteins functioning in the cytoplasm, the vacuole or in transport and transcription. Besides reduced poly P content, many strains also exhibited reduced total phosphate content, showed altered ATP and glycogen levels and were disturbed in the secretion of acid phosphatase.
  
  
  CONCLUSIONS
  Cellular energy and phosphate homeostasis is suggested to result from the equilibrium between poly P, ATP and free phosphate within the cell. Poly P serves as a buffer for both ATP and free phosphate levels and is, therefore, the least essential and consequently most variable component in this network. However, strains with reduced poly P levels are not only affected in their ATP and phosphate content, but also in other components that depend on ATP or free phosphate content, such as glycogen or secreted phosphatase activity.
authors.affiliation: Institute of Plant Sciences, ETH Zurich, 8092 Zurich, Switzerland. ffreimoser@ethz.ch
authors.forename: Florian M
authors.initials: FM
authors.lastname: Freimoser
authors.forename: Hans Caspar
authors.initials: HC
authors.lastname: Hürlimann
authors.forename: Claude A
authors.initials: CA
authors.lastname: Jakob
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Werner
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Amrhein
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D016000:Cluster Analysis; D004734:Energy Metabolism; D006003:Glycogen / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D011122:Polyphosphates / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism
chemical_list: D011122:Polyphosphates; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate; D006003:Glycogen; D000135:Acid Phosphatase