Ultrastructure analysis of membrane structures that accumulate in ESCRT mutant cells. (A) WT and mutant cells were starved for 2 h in SD-N (as in Fig. 2), fixed, and subjected to transmission EM. In addition to class E compartment, all single and double ESCRT mutant cells accumulate normal-sized APs (∼500 nm); red arrows point to the double membrane of an AP seen in the inset. Only pep4Δ single-mutant cells accumulate ABs inside their vacuole. E, class E compartment; Nuc, nucleus; Vac, vacuole; red asterisk, AP; black asterisk, AB. (B and C) Quantification of membrane structures that accumulate in mutant cells from A. (B) Percentage of cells with APs (black bars) or ABs (gray bar; bottom, number of cells used for quantification). (C) Number of APs (black bars) or ABs (gray bar) per cluster. Columns represent mean, error bars represent SD. Results in this figure represent three independent experiments. *P < 0.05; **P < 0.01.