It has been reported that Gap1p on the plasma membrane of Saccharomyces cerevisiae can catalyze the uptake of many kinds of amino acids. In the present study, we found that Gap1p also catalyzed the uptake of putrescine and spermidine, but not spermine. The K-m and V-max values for putrescine and spermidine were 390 and 21 muM, and 4.6 and 0.59 nmol/min/mg protein, respectively. The uptake of putrescine was strongly inhibited by basic amino acids, lysine, arginine, and histidine, whose K-i values were 2535 muM. Thus, it is deduced that spermidine and basic amino acids have almost the same affinity for Gap1p. When the concentrations of amino acids in the medium were reduced to one-third and 0.5 mM putrescine or 0.1 mM spermidine was added to the medium, accumulation of putrescine or spermidine by Gap1p was observed. Furthermore, when yeast was transformed with the GAP] gene and cultured in the presence of 60 mM putrescine, cell growth was inhibited through overaccumulation of putrescine. GAPI mRNA was found to be induced by polyamines. This is the first report of the identification, at a molecular level, of a polyamine uptake protein on the plasma membrane in eukaryotes. (C) 2005 Elsevier Inc. All rights reserved.