Coated vesicles transport newly synthesized membrane glycoproteins from endoplasmic reticulum to plasma membrane in two successive stages

Abstract

The G protein of vesicular stomatitis virus is a transmembrane glycoprotein that is transported from its site of synthesis in the rough endoplasmic reticulum to the plasma membrane via the Golgi apparatus. Clathrin-coated vesicles have been purified from CHO cells infected with vesicular stomatitis virus and shown to contain G protein in amounts nearly stoichiometric with clathrin. Pulse-chase experiments have demonstrated that this G protein is a transit form and have revealed that G is transported to the cell surface in two successive waves of coated vesicles. The oligosaccharides of G1 protein carried in the early wave are of the "high-mannose" variety which can be cleaved by the enzyme endoglycosidase H; the oligosaccharides of G2 protein in the second, later wave are resistant to endoglycosidase H. The early wave is therefore proposed to correspond to transport of G protein in coated vesicles from the endoplasmic reticulum to the Golgi apparatus, where the oligosaccharides are processed and resistance to endoglycosidase H is conferred; the succeeding wave would represent transport from the Golgi apparatus to the plasma membrane.