Figure 4. Transport activity of GeSUT4 in yeast.

(a) Growth assay of YSL2-1 cells expressing GeSUTs. Yeast cells expressing GeSUTs, an empty vector, and the AtSUC2 were seriously diluted and cultured on solid media (pH 5 or 7) supplemented with maltose or sucrose, respectively. Images were taken after incubation at 30 °C for 4-6 days. (b) Time-dependent uptake activity of YSL2-1 to sucrose. Yeast cells in (a) were incubated with 1 mM sucrose containing 1.5 μCi [14C]sucrose and then cells were harvested at indicated time point for radioactivity measurement. Significant differences from cells expressing the empty vector were determined. (c) Kinetic of GeSUT4 transport. Transformed cells were incubated in media containing indicated concentrations of sucrose with same molar ratio of [14C]sucrose. After 10 mins, cells were harvested and analyzed for radioactivity. (d) Substrate specificity ofGeSUT4 transport activity. Transformed cells were incubated for 10 mins with the control solution with or without 10 times concentrated sugars (Suc, sucrose; Glc, glucose; Gal, galactose; Fru, fructose; Man, mannose; Mal, maltose). Relative uptake rate was calculated compared to cells incubated with the control solution. The background uptake of non-transformed cells (empty) was also shown. Significant differences from cells incubated in the control solution were determined. (e) Effect of pH and protonophore on GeSUT4 uptake activity. Yeast cells expressing an empty vector, AtSUC2 or GeSUT4 were analyzed. Significant differences from results measured under the pH 5 condition were determined. Results are mean ± SE (n=3 in b, c, e or 5 in d).