Fig. 3.

Yeast growth complementation on and methylammonium plates by AQP1 mutants. (A) Expression control of AQP1 and mutants in 31019bΔmep1-3 (endogenous transporters deleted) by Western blotting. (B) 31019bΔmep1-3 expressing wild-type or mutant AQP1 were spotted at none, 1:10², and 1:10⁴ dilutions (left to right) on agar plates containing 3 mM (NH₄)₂SO₄ as a nitrogen source at the indicated pH values. Shown is the cell growth after 5 days. Here, cell growth indicates NH₃ uptake. (B) BY4742Δfps1 yeast (deletion of the endogenous aquaglyceroporin Fps1) expressing wild-type or mutant AQP1 spotted at none, 1:10, and 1:100 dilutions (left to right) on selective medium containing 0.1% proline as the nitrogen source and 100 mM cytotoxic methylammonium at the indicated pH values. Cell growth was monitored after 5 days. The isogenic parent strain BY4742 (top row) as well as sham-transformed BY4742Δfps1 yeast (second row) were used as controls. Cell growth indicates passage of methylamine through AQP1 mutants (see text for further explanations).