Restoration of resistance of <i>ZnT1</i>^−/−<i>MT</i>^−/−<i>ZnT4</i>^−/− cells by expression of the indicated genes against high zinc toxicity.

The relative contribution of hZnT1, mMt-I or hZnT4 re-expression in ZnT1−/−MT−/−ZnT4−/− cells against zinc toxicity was determined by counting the number of cells after 72 h exposure to the indicated concentrations of ZnSO4. The relative contribution of exogenous expression of hZnT2 or mutant hZnT1 or hZnT4 is also indicated. Relative values presented are evaluations of the averages of three independent experiments. ++: growing to confluence; +: less growth compared with ++ (20–50% relative to ++); -: not growing.