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

One novel feature of the rotavirus system is that the virus 2202 TNE JOURNAL OF CELL BIOLOGY -VOLUME 101, 1985 appears to be located primarily in elements of the ER (1). However, these earlier studies also showed that at 16 (Fig. 3) ; none were ever seen in the Golgi apparatus or in mitochondria. The viroplasm structures immediately adjacent to the RER were also evident and viral cores could be seen budding from the periphery of the viroplasm into the lumen of the RER. The envelope acquired from the RER membrane was subsequently lost and both enveloped and mature virions were visible in the lumenal space (Fig. 3) . VP7 has been located to the ER by immunoelectron microscopy (10, 32). In vitro translation studies have also shown it to be an integral membrane protein (2 I). Since the VP7 protein is found in mature virions and has only highmannose oligosaccharides (9), the data collectively show that VP7 remains in the ER after translation. However, the mechanism by which VP7 is incorporated into the virus remains unknown. Thus, the rotavirus VP7 provides an opportunity to study the factors controlling the specific localization of proteins to the ER.