ER domain ribosome density and distribution during inheritance. (A–D) 3D models of wt cells in order of bud size (as indicated). ER domains are color coded as in Fig. 1, and ribosomes are indicated as dots in the color of the ER domain to which they are bound. (E) The number of ribosomes per surface area was calculated for each domain in each of the wt mother cells. Bud size is shown on the bottom. (F) As in E for the bud. (G) A magnified 2D tomograph shows an ER tubule that is contacting a vacuole (red). Note the apparent lack of ribosomes (black dots) on the membrane. (H) The histogram shows the range of ER tubule diameters at the positions where ribosomes are bound (n = 65). (I) The mean tubER diameter at which ribosomes are bound (37.0 ± 1.1 nm; n = 65) is compared with the overall mean tubER diameters in the tubER population (37.9 ± 1.09 nm, from Fig. 3 E; n = 107). Brackets show the ranges, and boxes show the SEM. Horizontal lines indicate the means. cyto, cytoplasmic face. Bars: (A–D) 200 nm; (G) 50 nm.