FIGURE 14-17 Vesicle-mediated protein trafficking from the trans-Golgi network. COPI (purple) vesicles mediate retrograde transport within the Golgi (1). Proteins that function in the lumen or in the membrane of the lysosome are first transported from the trans-Golgi network via clathrin-coated (red) vesicles (3); after uncoating, these vesicles fuse with late endosomes, which deliver their contents to the lysosome. The coats on most clathrin-coated vesicles contains additional proteins (AP complexes) not shown here. Some vesicles from the trans-Golgi carrying cargo destined for the lysosome fuse with the lysosome directly (2), bypassing the late endosome. These vesicles are coated with a type of AP complex (blue); it is unknown whether these vesicles also contain clathrin. The coat proteins surrounding constitutive (4) and regulated (5) secretory vesicles have not yet been characterized; these vesicles carry secreted proteins and plasma-membrane proteins from the trans-Golgi network to the cell surface.