INTRACELLULAR SEQUESTRATION OF SODIUM BY A NOVEL NA+ H+ EXCHANGER IN YEAST IS ENHANCED BY MUTATIONS IN THE PLASMA-MEMBRANE H+-ATPASE - INSIGHTS INTO MECHANISMS OF SODIUM TOLERANCE/
R. Nass et al., INTRACELLULAR SEQUESTRATION OF SODIUM BY A NOVEL NA+ H+ EXCHANGER IN YEAST IS ENHANCED BY MUTATIONS IN THE PLASMA-MEMBRANE H+-ATPASE - INSIGHTS INTO MECHANISMS OF SODIUM TOLERANCE/, The Journal of biological chemistry, 272(42), 1997, pp. 26145-26152
Sodium tolerance in yeast is disrupted by mutations in calcineurin, a
Ca2+/calmodulin dependent protein phosphatase, which is required for m
odulation of Na+ uptake and efflux mechanisms, Five Na+-tolerant mutan
ts were isolated by selecting for suppressors of calcineurin mutations
, and mapped to the PMA1 gene, encoding the plasma membrane H+-ATPase,
One mutant, pma1-alpha 4, which has the single amino acid change Glu(
367) --> Lys at a highly conserved site within the catalytic domain of
the ATPase, was analyzed in detail to determine the mechanism of Natolerance. After exposure to Na+ in the culture medium, Na-22 influx i
n the pma1 mutant was reduced 2-fold relative to control, consistent w
ith a similar decrease in ATPase activity, Efflux of Na-22 from intact
cells was relatively unchanged in the pma1 mutant, However, selective
permeabilization of the plasma membrane revealed that mutant cells re
tained up to 80% of intracellular Na+ within a slowly exchanging pool,
We show that NHX1, a novel gene homologous to the mammalian NHE famil
y of Na+/H+ exchangers, is required for Na+ sequestration in yeast and
contributes to the Na+-tolerant phenotype of pma1-alpha 4.