Identification of a gene for a polyamine transport protein in yeast

Properties of a membrane protein encoded by YLL028w were examined using yea st cells transformed with the gene. The transformed cells became resistant to polyamine toxicity, and the resistance was overcome by bafilomycin A(1), an inhibitor of vacuolar H+-ATPase. Although spermine uptake activity of t he transformed cells was almost the same as that of wild type cells, the up take activity of vacuolar membrane vesicles from the transformed cells was higher than that from wild type cells. The transformed cells became resista nt to MGBG (methylglyoxal bis(guanylhydrazone)) and paraquat, but not Ni2and Co2+, suggesting that the protein encoded by YLL028w is a transport pro tein specific for polyamines. When the YLL028w gene was disrupted by insert ing the HIS3 gene, the cells became sensitive to polyamines, and spermine u ptake activity of the vacuolar membrane vesicles decreased significantly. T he accumulated spermine in YLL028w gene-disrupted cells decreased greatly c ompared with that in wild type cells. The results indicate that a membrane protein encoded by YLL028w (TPO1) is a polyamine transport protein on the v acuolar membrane.