ERG30, a VAP-33-related protein, functions in protein transport mediated by COPI vesicles

Intracellular transport of newly synthesized and mature proteins via vesicl es is controlled by a large group of proteins. Here we describe a ubiquitou s rat protein-endoplasmic reticulum (ER) and Golgi 30-kD protein (ERG30)-wh ich shares structural characteristics with VAP-33, a 33-kD protein from Apl ysia californica which was shown to interact with the synaptic protein VAMP . The transmembrane topology of the 30-kD ERG30 corresponds to a type II in tegral membrane protein, whose cytoplasmic NH2 terminus contains a predicte d coiled-coil motif. We localized ERG30 to the ER and to pre-Golgi intermed iates by biochemical and immunocytochemical methods. Consistent with a role in vesicular transport, anti-ERG30 antibodies specifically inhibit intra-G olgi transport in vitro, leading to significant accumulation of COPI-coated vesicles. It appears that ERG30 functions early in the secretory pathway, probably within the Golgi and between the Golgi and the ER.