Abstract
COP‐coated vesicles have originally been implicated in vesicular transport between subcompartments of the Golgi complex in mammals in a cis to trans direction. More recently, a role for COP‐coated vesicles in transport between the endoplasmic reticulum (ER) and Golgi in mammalian cells has been proposed. Under certain conditions COP‐coats have been localized to special domains of the transitional ER and to the cis side of the Golgi complex. This led to the assumption that COP‐coated vesicles are involved in export of proteins from the ER. In addition, new findings point to a function of COP‐coated vesicles in back transport of proteins from the Golgi to the ER. At present it is not known whether COP‐coated vesicles move only in one or in both directions between ER and Golgi.