Large Mg(2+)-dependent currents are associated with the increased expression of ALR1 in Saccharomyces cerevisiae

Two genes in Saccharomyces cerevisiae, ALR1 and ALR2, encode proteins putatively involved in Mg(2+) uptake. The present study supports this role for ALR1 and provides the first electrophysiological characterisation of this protein. The patch-clamp technique was used to measure whole-cell ion currents in protoplasts prepared from the wild-type strain, the alr1 alr2 double mutant (CM66), and the double mutant over-expressing the ALR1 gene (CM66+ALR1). With 50 mM Mg(2+) in the bathing solution, the inward current in protoplasts of CM66+ALR1 averaged -264+/-48 pA at -150 mV. Inward currents measured in the wild-type and CM66 protoplasts were more than five-fold smaller. When Mg(2+) was the major cation in the pipette solution, time-dependent outward currents were also detected in CM66+ALR1 protoplasts suggesting ALR1 can facilitate Mg(2+) efflux as well as uptake. We conclude that the ALR1 gene encodes a transport protein. The large magnitude of the Mg(2+)-dependent currents suggests that ALR1 could function as a cation channel.