Because the diameter of COPII-coated tubules is below the optical resolution of confocal microscopy, we used EM for a more detailed examination. Cryo-EM revealed that the COPII-coated tubules carry symmetric constrictions at regular intervals (Fig. 3). In other words, they consist of unfissioned vesicles, like beads on a string. The size of the connected vesicles in cryo-EM was rather homogeneous (Fig. 3a–h), although variations occurred, for instance at the end of a string (Fig. 3e). Apart from the prominent connected protein-coated vesicles, single vesicles as well as larger liposomes were observed (Fig. 3a,d–h).