Fig. 1.

The conundrum: In wild-type yeast cells, actin and BAR proteins turn a shallow invagination into a mature vesicle with a narrow tubular domain before scission (lipid membrane is shown in yellow, clathrin coat in red, actin filaments in blue, and BAR coat in green). In BAR mutant yeast cells, the intermediate vesicle with a constricted neck is not observed. A detached vesicle is directly seen after an initial broad invagination. Because a nonleaky scission requires lipids to come in close proximity and transition through a hemifission state, how broad and shallow invaginations undergo scission remains intriguing. This puzzle is at the core of this study. The figure is not drawn to scale.