Regulation of monovalent ion homeostasis and pH by the Ser-Thr protein phosphatase SIT4 in Saccharomyces cerevisiae.
A gene, SIT4, was identified as corresponding to a serine/threonine protein phosphatase and when overexpressed confers lithium tolerance in galactose medium to the budding yeast Saccharomyces cerevisiae. This gene has been previously identified as a regulator of the cell cycle and involved in nitrogen sensing. It is shown that the transcription levels of SIT4 are induced by low concentrations of Li(+) in a time-dependent manner. Na(+) and K(+) at high concentrations, but not sorbitol, also induce transcription. As a response to Na(+) or Li(+) stress, yeast cells lower the intracellular K(+) content. This effect is enhanced in cells overexpressing SIT4, which also increase (86)Rb efflux after the addition of Na(+) or Li(+) to the extracellular medium. Another feature of SIT4-overexpressing cells is that they maintain a more alkaline pH of 6.64 compared with 6.17 in the wild type cells. It has been proposed that the main pathway of salt tolerance in yeast is mediated by a P-type ATPase, encoded by PMR2A/ENA1. However, our results show that in a sit4 strain, expression of ENA1 is still induced by monovalent cations, and overexpression of SIT4 does not alter the amount of ENA1 transcript. These results show that SIT4 acts in a parallel pathway not involving induction of transcription of ENA1 and suggest a novel function for SIT4 in response to salt stress.
Masuda
C A
CA
Departamento de Bioquimica Médica, ICB-CCS, Universidade Federal do Rio de Janeiro, Rio de Janeiro, R.J. 21941-590, Brazil.
Ramírez
J
J
Peña
A
A
Montero-Lomelí
M
M
D000251:Adenosine Triphosphatases / Q000378:metabolism; D027682:Cation Transport Proteins; D002412:Cations; D002453:Cell Cycle / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D005690:Galactose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000378:metabolism* / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D054648:Protein Phosphatase 2; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012414:Rubidium Radioisotopes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins; D012964:Sodium / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase; D013012:Sorbitol / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic
D027682:Cation Transport Proteins; D002412:Cations; C086375:ENA1 protein, S cerevisiae; D007477:Ions; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012414:Rubidium Radioisotopes; D029701:Saccharomyces cerevisiae Proteins; D012965:Sodium Chloride; D013012:Sorbitol; D008094:Lithium; D012964:Sodium; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C104343:SIT4 protein, S cerevisiae; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase; D018021:Lithium Chloride; D011188:Potassium; D005690:Galactose