Figure 1.

Mitochondrial constriction and division occurs at ER-mitochondrial contacts in yeast. (A) 3-D models (left panels) of ER (green) and mitochondria (purple) at contact domains were imaged by EM and tomography of high pressure frozen yeast cells. Middle two panels are 2-D tomographs of contact sites (second panels, ER drawn in green) and the corresponding 3-D models of each (third panels). Contact is defined as regions where the ER membrane comes within 30 nm of the mitochondrial membrane and ribosomes are excluded, and is outlined in red (third panel). Right panel is a schematic demonstrating the percentage of the mitochondrial circumference that makes contact with the ER membrane (red is contact, white is not; (19)). The diameter of each mitochondrion at positions of ER contact is shown. Note that regions where the mitochondria are constricted (models a and c) have a high percent of ER wrapping. Additional EM tomographs and analysis of constrictions are shown in Fig. S1A–B. (B) Time-lapse images of yeast cells expressing mito-dsRED and GFP-HDEL (ER). A single focal plane is shown. Arrows indicate sites of mitochondrial division. Corresponding z-series is shown in Fig. S1C. Scale bars: (A) 200 nm; (B) 2 µm.