Extended Data Fig. 4 |. The expression of TMHC6 complements a yeast strain defective of K⁺ uptake.

(a) SGY1528 with an empty vector MCS grew slowly when K⁺ concentration was lower than 5 mM. Observed growth rate showed dependency on extracellular K⁺ concentration. (b) SGY1528 supplemented with the TMHC6 gene rescued the yeast growth at lower extracellular K⁺ concentrations (1 mM - 5 mM) and showed increased growth rates at higher extracellular K⁺ concentrations (7.5 mM - 100 mM). (c & d) With increasing concentrations of extracellular Na⁺, TMHC6 yeast showed decreased growth rate (d) in comparison with the insensitive growth rates of MCS yeast (c). These results suggest that TMHC6 conducts K⁺ and complements the defective K⁺ uptake in strain SGY1528; this rescuing effect is sensitive to extracellular Na⁺ concentrations indicating an increased Na⁺ permeability. A detailed method section is described in Supplementary Materials. The minimal medium and the seeding process are carefully designed to not contain or bring in potassium. The background K⁺ concentration should be low, which is suggested by the sharp difference between curves for 0 and 1 mM K⁺ in the TMHC6 case.