Export of Proteins and Lipids from the ER
Both proteins and lipids travel along the secretory pathway in transport vesicles, which bud from the membrane of one organelle and then fuse with the membrane of another. Thus, molecules are exported from the ER in vesicles that bud from the ER and carry their cargo first to the ER-Golgi intermediate compartment and then to the Golgi apparatus (Figure 9.20).
Figure 9.20. Vesicular transport from the ER to the Golgi Proteins and lipids are carried from the ER to the Golgi in transport vesicles that bud from the membrane of the ER and then fuse to form the vesicles and tubules of the ER-Golgi intermediate compartment (ERGIC). Lumenal ER proteins are taken up by the vesicles and released into the lumen of the Golgi. Membrane proteins maintain the same orientation in the Golgi as in the ER.