Deletions into an NH2-terminal hydrophobic domain result in secretion of rotavirus VP7, a resident endoplasmic reticulum membrane glycoprotein

To accurately interpret the localization of expressed VP7 protein products within COS 7 cells, it was necessary to examine the ultrastructural morphology and interrelationships of organelles in COS 7 cells, especially in the perinuclear region. These cells are characterized at their periphery by predominantly free polysomes crowding the cytoplasm and by numerous microvilli projecting from their cell surface (Fig. 4) . The cells are often multinucleate, have many lipid droplets, mitochondria, and a preponderance of organelles situated close to each other around the nucleus at the center of the cell (Fig. 4, a and b) . The perinuclear region is occupied by extensive branching ER, which contains numerous areas of transitional elements (Fig. 4 and inset) and smooth ER that spatially intertwine with, but are distinct from, the extensive perinuclear Golgi apparatus. It is evident that portions of the Golgi apparatus can surround concentrated elements of the ER.