Fig. 5. Defective endocytic acidification does not cause all defects in btn1 cells. (A) Acidic medium does not rescue the cytokinesis defects of btn1 cells. Graph of septation indices of btn1 cells grown at 25°C in YES medium at pH 6, pH 4, or pH 6 + 1 M sorbitol. n=200 for each group (at least two replicates). (B) Acidic medium does not rescue septum thickness. Graph of septum thickness of btn1 cells grown at the indicated pH (n=6 for each) as determined by EM. (C) Acidic medium does not rescue cell death and/or lysis of btn1 cells at 37°C. (i) Phase-contrast images of btn1 cells grown for 18 hours in YES medium at pH 4. (ii) Graph of the number of cell cycles completed by 18 hours by btn1 cells grown in YES medium at pH 6, pH 4, or pH 6 + 1 M sorbitol. n=200 for each group (at least two replicates). (D) vma1 cells grow slowly but do not have cytokinesis defects or a swollen phenotype at 37°C. (i) YES plate showing wild-type, vma1 and btn1vma1 cells grown for 3 days at 37°C. (ii) Phase-contrast images of the same vma1 cells as in Di. (E) btn1vma1 cells have a severe cytokinesis defect. (i) Graph of septation indices of cells grown at the indicated temperatures. n=200 for each group (at least two replicates). (ii) Calcofluor-stained septa of vma1 and btn1vma1 cells grown at 37°C for 4 hours. Note the multiple septa in btn1vma1 cells. Scale bars: 10 µm.