A genetic analysis of the role of calcineurin and calmodulin in Ca++-dependent improvement of NaCl tolerance of Saccharomyces cerevisiae.
Mutants of Saccharomyces cerevisiae lacking activity of the Ca2+/calmodulin-dependent protein phosphatase calcineurin, show sensitivity to high concentrations of sodium that is partly reversed by the external supply of Ca2+. On long-time exposure to NaCl stress the mutants display an increased intracellular Na+/K+ ratio which is partially corrected by the addition of Ca2+, improving the sodium efflux of not only calcineurin-defective cells but also wild-type cells. We also demonstrate that the NaCl sensitivity of cmd mutants, expressing modified forms of calmodulin that do not bind Ca2+, is strongly reversed by the addition of Ca2+. This effect is highly dependent on calcineurin, since the NaCl tolerance of a cmd1-3 strain, carrying an additional mutation in calcineurin, is only slightly assisted by Ca2+. A striking characteristic of the loss of function of calcineurin is a several-fold increased content of intracellular Ca2+, localized mainly in subcellular compartment(s). If the compartmentalized Ca2+ pool is brought back to normal levels by an additional inactivating mutation of the vacuolar Ca2+-transporting ATPase, such double mutants do not significantly improve their tolerance to NaCl.
Danielsson
A
A
Department of General and Marine Microbiology, University of Göteborg, Lundberg Laboratory, Medicinaregatan 9C, S-431 90 Göteborg, Sweden.
Larsson
C
C
Larsson
K
K
Gustafsson
L
L
Adler
L
L
D019703:Calcineurin; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000235:genetics / Q000502:physiology*; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000502:physiology*; D002451:Cell Compartmentation; D005990:Glycerol / Q000378:metabolism; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*; D014882:Water-Electrolyte Balance
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D012965:Sodium Chloride; D012964:Sodium; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D005990:Glycerol; D011188:Potassium; D002118:Calcium