Reconstitution of transport of vesicular stomatitis virus G protein from the endoplasmic reticulum to the Golgi complex using a cell-free system

Transport of the vesicular stomatitis virus-encoded glycoprotein (G protein) between the endoplasmic reticulum (ER) and the cis Golgi compartment has been reconstituted in a cell-free system. Transfer is measured by the processing of the high mannose (man_8-9GlcNAc₂) ER form of G protein to the man₅GlcNAc₂ form by the cis Golgi enzyme α-mannosidase I. G protein is rapidly and efficiently transported to the Golgi complex by a process resembling that observed in vivo. G protein is trimmed from the high mannose form to the man₅GlcNAc₂ form without the appearance of the intermediate man_6-7GlcNAc₂ oligosaccharide species, as is observed in vivo. G protein is found in a sealed membrane-bound compartment before and after incubation. Processing in vitro is sensitive to detergent, and the Golgi α-mannosidase I inhibitor 1-deoxymannorjirimycin. Transport between the ER and Golgi complex in vitro requires the addition of a high speed supernatant (cytosol) of cell homogenates, and requires energy in the form of ATP. Efficient reconstitution of export of protein from the ER requires the preparation of homogenates from mitotic cell populations in which the nuclear envelope, ER, and Golgi compartments have been physiologically disassembled before cell homogenization. These results suggest that the high efficiency of transport observed here may require reassembly of functional organelles in vitro.