FORMATION OF SECRETORY VESICLES IN PERMEABILIZED CELLS - A SALT EXTRACT FROM YEAST MEMBRANES PROMOTES BUDDING OF NASCENT SECRETORY VESICLESFROM THE TRANS-GOLGI NETWORK OF ENDOCRINE-CELLS

The mechanism of secretory-vesicle formation from the trans-Golgi netw ork (TGN) of endocrine cells is poorly understood. To identify cytosol ic activities that facilitate the formation and fission of nascent sec retory vesicles, we treated permeabilized pituitary GH(3) cells with h igh salt to remove endogenous budding factors. Using this cell prepara tion, secretory-vesicle budding from the TGN required addition of exog enous cytosol and energy. Mammalian cytosols (GH(3) cells and bovine b rain) promoted post-TGN vesicle formation. Most significantly, a salt extract of membranes from the yeast Saccharomyces cerevisiae, a cell l acking a regulated secretory pathway, stimulated secretory vesicle bud ding in the absence of mammalian cytosolic factors. These results demo nstrate that the factors which promote secretory-vesicle release from the TGN are conserved between yeast and mammalian cells.