3D ER domain structure in mutant Δrtn1rtn2yop1. (A and B) 3D models showing ER domain organization at two different angles of a mutant cell (mutant = Δrtn1rtn2yop1) with a 596-nm bud (A) and a 1,253-nm bud (B). (C and D) 3D model of a wt cell with a 665-nm bud (C) and a 1,255-nm bud (D) to compare with mutants. All ER domains are color coded as in Fig. 1. (E) Graph comparing the volume of each peripheral ER domain found within the reconstructed volume of the mutant mother cell (in A and B) compared with that of wt cells (C and D) with similar bud sizes. (F) As in E for the bud. (G) Comparison of mean diameters for wt and mutant ER domains showing differences in diameters/thickness that are significant for tubER and pmaER but not for NE. Horizontal lines indicate mean diameters given above the boxes. Mutant tubER mean diameter = 45.8 ± 1.6 nm versus 37.9 ± 1.1 nm for wt; mutant pmaER mean thickness = 30.3 ± 0.44 nm versus 35.6 ± 0.74 nm in wt (both are significant by unpaired t test; **, P < 0.0001). NE mutant mean thickness = 29.5 ± 0.6 nm versus 28.5 ± 0.6 nm for wt (not significantly different; P = 0.28). Brackets show range of measurements, and boxes show SEM. (H) Lengthwise diameters of nine different wt tubules and seven different mutant tubules. (I) 3D models were used to calculate the surface area of pmaER and PM to determine the percentage of the PM covered by the pmaER for wt and mutant cells. Blue and green percentages show comparisons between the wt and mutant cells with similar bud sizes. Bud sizes are indicated below each graph. Mut, mutant. SA, surface area. Bars, 200 nm.