Identification of the fnx1+ and fnx2+ genes for vacuolar amino acid transporters in Schizosaccharomyces pombe

We have identified the Schizosaccharomyces pombe SPBC3E7.06c gene (fnx2+) from a homology search with the fnx1+ gene involving in G0 arrest upon nitrogen starvation. Green fluorescent protein-fused Fnx1p and Fnx2p localized exclusively to the vacuolar membrane. Uptake of histidine or isoleucine by S. pombe cells was inhibited by concanamycin A, a specific inhibitor of the vacuolar H+-ATPase. Amino acid uptake was also defective in the vacuolar ATPase mutant, suggesting that vacuolar compartmentalization is critical for amino acid uptake by whole cells. In both Δfnx1 and Δfnx2 mutant cells, uptake of lysine, isoleucine or asparagine was impaired. These results suggest that fnx1+ and fnx2+ are involved in vacuolar amino acid uptake in S. pombe.