Molecular model of mitochondrial division. T op: mitochondrial division is depicted as a linear pathway with the relative rates of each step (1–3) indicated. Red circles represent Dnm1p-containing complexes. Bottom: the postulated molecular interactions occurring between Dnm1p, Fis1p and Mdv1p during steps 1 and 2 of the pathway. Mitochondrial tubules are drawn in cross section and a single complex is shown containing the three molecules. Dnm1p, Mdv1p and Fis1p are shown in red, blue, and green, respectively. Abbreviation: IMS, intermembrane space.