Fig 4.

Influence of mutation of a conserved serine residue on ammonium uptake rate of yeast strain MLY131a/α (mep1-3Δ) expressing yeast (control) or Geosiphon pyriformis AMTs. The respective wild-type constructs are indicated in boldface. Serine-to-cysteine mutation of GpAMT1 reduced its transport capacity, while cysteine-to-serine mutation of GpAMT2 increased its transport capacity; as expected, no effect of cysteine-to-serine mutation was detected for GpAMT3, which is located at the vacuole membrane. Uptake rates were determined by an ammonium removal assay in the presence of 1 mM NH₄⁺. Error bars, ±standard deviation; n = 3 biological replicates. Statistical differences were calculated using Student's t test (*, P ≤ 0.05; **, P ≤ 0.01). No significant differences were found between ScMEP2 S₁₉₇ and S₁₉₇C or GpAMT3 C₁₈₉S and C₁₈₉ strains.