FIG 5.
Efr3, Ypp1, and Stt4 are critical for plasma membrane PI(4)P. (A) Strains expressing the plasma membrane PI(4)P reporter, GFP-Osh2PH-Osh2PH-GFP (wild type, PY2626; efr3Δ/Δ, PY4947; ypp1Δ/Δ, PY3950; stt4Δ/Δ, PY5169; stt4Δ/Δ+stt4*, PY5838) were imaged, and central z-sections of representative cells are shown with an inverted lookup table (LUT). Bar, 5 μm. (B and C) Quantitation of plasma membrane and internal signals reveals little to no plasma membrane PI(4)P in the stt4 mutant. The ratio of plasma membrane to internal signal (normalized to the wild type) and the relative plasma membrane signal (normalized plasma membrane/total signal) is shown. Quantitation of plasma membrane and internal signals was carried out excluding Golgi cisternae. For the wild type, the mean ratio of plasma membrane to internal signal was 3.8 and the ratio of plasma membrane to total signal was 0.8. We were able to detect ∼1.5% of wild-type plasma membrane PI(4)P levels. Smaller symbols are values from two experiments (6 to 15 cells per experiment), and larger symbols are means for each experiment, with bars indicating overall means and standard deviations. ****, P < 0.0001.