The 50-nm Free Vesicles Visible in Saccharomyces cerevisiae Are Not COPII-Dependent.

According to the current dogma, ER-Golgi transport is mediated by COPII-coated vesicles. However, numerous contradictions have emerged in this field. In this study, we demonstrate that Saccharomyces cerevisiae contains three distinct types of membrane spheres, with diameters of approximately 35-45 nm, 47-52 nm, and over 65 nm, respectively. The first type is Sso1-positive and primary associated with clathrin-positive endocytosis invaginations, which may function as exit sites for secretory soluble cargos. The second population is GOS1-positive and COPI-dependent. The third population represents secretory granules. Furthermore, we propose that several cornerstone studies supporting the COPII-vesicle model can have alternative interpretations. Our findings suggest that the predominant model of intracellular transport in Saccharomyces cerevisiae is the "kiss-and-run" mechanism.