Stm1 is a vacuolar PQ-loop protein involved in the transport of basic amino acids in Schizosaccharomyces pombe

The stm1+ (SPAC17C9.10) gene of Schizosaccharomyces pombe is closely related to genes encoding vacuolar PQ-loop proteins, Ypq1, Ypq2, and Ypq3, of Saccharomyces cerevisiae. When stm1+ fused with GFP was expressed in fission or budding yeast, Stm1-GFP localized at the vacuolar membrane. Isolated vacuolar membrane vesicles from S. cerevisiae cells overexpressing stm1+ exhibited stm1+-dependent arginine and lysine uptake activity. Exchange activity of arginine and histidine/arginine, as observed for Ypq2 of S. cerevisiae, was also detected in the vesicles expressing stm1+. The expression levels of stm1+ in S. pombe cells significantly affected the vacuolar contents of lysine, histidine, and arginine. These results suggest that Stm1 is a vacuolar PQ-loop protein involved in the transport of basic amino acids across the vacuolar membrane. Transport of amino acids across the vacuolar membrane of fission yeast, Schizosaccharomyces pombe. [Display omitted] •Stm1 of the fission yeast Schizosaccharomyces pombe is a vacuolar PQ-loop protein.•Transport activities of basic amino acids were detected with isolated vacuolar membrane vesicles expressing stm1+.•Stm1 is required for the amino acid compartmentalization in vacuoles of fission yeast.