Figure 7.

Inactivation of Slt2p, but not Hog1p, suppresses the ER inheritance defects in ptc1 and nbp2 mutant cells. (A) Both Ptc1p and Nbp2p have been implicated in the CWI MAPK pathway (Huang and Symington, 1995; Ohkuni et al, 2003). Protein kinase C (Pkc1p) acts as an upstream activator of this MAPK cascade. Deletion of ptc1 suppresses mutant phenotypes of pkc1–4 cells whereas deletion of either mkk1 or mkk2 suppresses the ts phenotype of nbp2Δ cells. (B) Deletion of slt2, but not hog1, restored ER inheritance in the ptc1Δ mutant. Shown are representative fluorescence and fluorescence-DIC merged images of the ER distribution in ptc1Δ slt2Δ buds and ptc1Δ hog1Δ cells grown to early log phase in SC medium at 25°C. (C) The ER inheritance defects in ptc1Δ and nbp2Δ cells was suppressed by sorbitol. Isogenic wild-type (SFNY1255), ptc1Δ (SFNY1610), and nbp2Δ (SFNY1685) strains were grown to early log phase and divided into two aliquots. Half the cells were grown at 25°C for 3 h in SC medium in the absence (−sorbitol) or presence of 1 M sorbitol (+sorbitol). Representative fluorescence and fluorescence-DIC merged images of cells with small (open arrow heads), medium (arrow heads), and large buds (arrows) are shown. The open arrow in the first row indicates a new wild-type bud. Quantitation revealed that the deletion of slt2 (D) and sorbitol treatment (E) leads to significant suppression. Key: 117 ptc1Δ slt2Δ buds (), 139 ptc1Δ hog1Δ buds (–○–), 278 wild-type buds cultured in SC+1 M sorbitol (–⧫–), 275 ptc1Δ buds grown in SC medium (), 284 ptc1Δ buds grown in SC+1 M sorbitol (), 296 nbp2Δ buds grown in SC medium (–▵–), 284 nbp2Δ buds grown in SC+1 M sorbitol (–▴–) were analyzed. (F) Deletion of slt2 had no effect on vacuole distribution in ptc1Δ mutant and wild-type cells. The vacuole inheritance defect was analyzed as in Figure 3B. Bars, 5 μm.