On vesicle formation and tethering in the ER-Golgi shuttle.

Transport in the ER-Golgi shuttle is performed by COPII in the anterograde and by COPI in the retrograde direction. How these transport steps are regulated and which mechanisms act to balance the vesicle flow between the ER and the Golgi apparatus are the issues currently under investigation. The elucidation of the structures of COPII components and tethers for COPI and COPII vesicles, together with detailed biochemical and cell biological analysis over the past few years greatly increased our knowledge on how vesicles are formed, not only at the ER and the Golgi but also at other organelles and the plasma membrane by analogy. Moreover, recent work provided more than just a glimpse on the function of tethering proteins at arrival sites on the ER and the Golgi. Most likely, organized exit and arrival sites exist at each vesicular transport step along the exocytic and endocytic routes.