Figure 7.

(A) Cells bearing the yip1-4 allele are thermosensitive. yip1-4 mutant cells bearing the single point mutation E70K are thermosensitive with a restrictive temperature of 34°C on rich media. Growth of yip1-4 cells on YPD are compared with isogenic wild-type controls at the temperatures indicated. (B–E) yip1-4 mutant cells are defective in Golgi localization of the Rab protein Ypt1p at the restrictive temperature. The localization of GFP-Ypt1p was measured in yip1-4 mutant and wild-type cells following a shift to the restrictive temperature (37°C) for the time indicated. The cells were visualized by fluorescence microscopy. The left side of each panel shows GFP fluorescence, whereas the right side is differential interference contrast optics. The characteristic punctate Golgi distribution of GFP-Ypt1p becomes diffuse and cytosolic after only a 10-min shift to the restrictive temperature and becomes maximal by 30 min of shift. This is in contrast to another peripheral Golgi marker, Sec7p, which maintains characteristic Golgi puncta at restrictive temperatures in yip1-4 cells. (B) yip1-4 mutant cells (RCY1764) expressing GFP-Ypt1p after shift to restrictive temperature for the times indicated. (C) isogenic wild-type cells (RCY1768) expressing GFP-Ypt1p after shift to restrictive temperature for the times indicated. (B) yip1-4 mutant cells (RCY1764) expressing Sec7p-DsRed after shift to restrictive temperature for the times indicated. Sec7p-DsRed after shift to restrictive temperature for the times indicated.