Figure 4.

Mutation of the Lipid Binding Site at the UapA Dimer Interface Results in Loss of Transport Function

The constructs were transformed into the A. nidulans strain (uapAΔ uapCΔ azgAΔ pabaA1 argB2). uapAΔ indicates the original recipient strain as a negative control.

(A) Growth tests of A. nidulans strains in minimal media supplemented with either ammonium (NH₄⁺), uric acid (Ua), or xanthine (Xa) as the nitrogen source. Growth was assessed at 37°C and 25°C.

(B) Inverted fluorescence microscopy images showing localization of the GFP-tagged UapA constructs. All mutants display normal sorting to the membrane. Scale bar corresponds to 5 μm.

(C) [³H]Xanthine uptake assays, with rate of WT UapA uptake defined as 100%.

(D) Table of K_M values of the UapA mutants. The fungal growth and localization data are representative of three independent experiments carried out under identical conditions. The K_M and fluorescence quantification data are the average ± SD, n = 3.