IDENTIFICATION OF AN INTERMEDIATE COMPARTMENT INVOLVED IN PROTEIN-TRANSPORT FROM ENDOPLASMIC-RETICULUM TO GOLGI-APPARATUS

We have studied the role of previously described tubulovesicular compartment near the cis-Golgi apparatus in endoplasmic reticulum (ER)-to-Golgi protein transport by light and immunoelectron microscopy in Vero cells. The compartment is defined by a 53-kDa transmembrane protein designated p53. When transport of the vesicular stomatitis virus strain ts945 G protein was arrested at 39.5-degrees-C, the G protein accumulated in the ER but had access to the p53 compartment. At 15-degrees-C, the G protein was exported from the ER into the p53 compartment which formed a compact structure composed of vesicular and tubular profiles in close proximity to the Golgi. Upon raising the temperature to 32-degrees-C, the G protein migrated through the Golgi. Upon raising the temperature to 32-degrees-C, the G protein migrated through the Golgi apparatus while the p53 compartment resumed its normal structure again. These results establish the p53 compartment as the 15-degrees-C intermediate of the ER-to-Golgi protein transport pathway.