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

endo-H-resistant products secreted into the medium by these mutants contain an N-linked complex type of carbohydrate. Secreted VP7 c was again observed to be endo-H-resistant (data not shown) and to be present in approximately the same amount as the internal endo-H-sensitive VP7 (Fig. 8, lanes 5 and 7) . In order to understand the specificity in the location of membrane glycoproteins, we have used a glycoprotein that is located in the ER in its natural state. ER location implies either the presence of a targeting signal specific for the ER or the absence of a positive signal that would otherwise direct the protein elsewhere. The structural glycoprotein VP7, of the rotavirus SA11, provides just such a naturally targeted ER protein. It is a membrane glycoprotein (21) before assembly into virus. How the transfer of the glycoprotein takes place is not known and we know of no other animal virus which exhibits this behavior. However, the mode of transfer of membrane protein to the virus particle resembles the assembly of coat protein into the filamentous phage M 13 (44) .