UDP-Galf binds to GlfB. A, [3H]UMP uptake by Golgi vesicles isolated from yeast expressing GlfB (black bars) or the human UDP-Gal transporter (gray bars) in the absence or presence of a 100-fold molar excess of unlabeled UMP, UDP-Galf (containing 7% UMP), UDP-Gal, or UDP-GlcNAc. B, comparison of [3H]UMP uptake in the presence of a 100 m excess UDP-Galf containing 7% UMP or an 8 m excess UMP. Each value represents the average of three independent experiments with duplicate measurements. ns, not significant.