The ZRT2 gene encodes the low affinity zinc transporter in Saccharomyces cerevisiae

Zinc accumulation in Saccharomyces cerevisiae occurs through either of two uptake systems. A high affinity system is active in zinc-limited cells, and the ZRT1 gene encodes the transporter protein of this system. In this study, we characterized the low affinity system that is active in zinc-replete cells. The low affinity system is time-, temperature-, and concentration-dependent and prefers zinc over other metals as its substrate. Our results suggest that the ZRT2 gene encodes the transporter of this system. The amino acid sequence of Zrt2p is remarkably similar to those of Zrt1p and Irt1p, an Fe2+ transporter from Arabidopsis thaliana. Overexpressing ZRT2 increased low affinity uptake, whereas disrupting this gene eliminated that activity, but had little effect on the high affinity system. Therefore, the high and low affinity systems are separate uptake pathways. Analysis of the zinc levels required for growth of zrt2 mutant strains as well as the effects of the zrt2 mutation on the regulation of the high affinity system demonstrated that the low affinity system is a biologically relevant mechanism of zinc accumulation. Finally, a zrt1zrt2 mutant was viable, indicating the existence of additional zinc uptake pathways.