Uptake of GABA and putrescine by UGA4 on the vacuolar membrane in Saccharomyces cerevisiae

The product of the UGA4 gene in Saccharomyces cerevisiae, which catalyzes the transport of 4-aminobutyric acid (GABA), also catalyzed the transport of putrescine. The Km values for GABA and putrescine were 0.11 and 0.69 mM, respectively. The UGA4 protein was located on the vacuolar membrane as determined by the effects of bafilomycin A1 and by indirect immunofluorescence microscopy. Uptake of both GABA and putrescine was inhibited by spermidine and spermine, although these polyamines are not substrates of UGA4. The UGA4 mRNA was induced by exposure to GABA, but not putrescine over 12h. The growth of an ornithine decarboxylase-deficient strain was enhanced by putrescine, and both putrescine and spermidine contents increased, when the cells were expressing UGA4. The results suggest that a substantial conversion of putrescine to spermidine occurs in the cytoplasm even though UGA4 transporter exists on vacuolar membranes.