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

The key observation is that in three of the deletion mutants extending into the second hydrophobic region, namely mutants 42-61, 43-61, and 47-61, the altered form of VP7 is secreted by transfected COS 7 cells and terminally glycosylated, a characteristic of a protein having traversed the normal secretory pathway. By contrast, neither the wild-type gene product was secreted, nor were products from deletions which affected other parts of the molecule. The deletion 1-14, which completely removed the first hydrophobic domain and mutant 2-8, in which the eight amino terminal residues conserved in all four rotavirus VP7 serotypes (9) were changed (see Materials and Methods), efficiently expressed glycoprotein located to the ER. Similarly, removal of only 11 amino acids downstream of the hydrophobic domains in mutant 51-6 l, apparently was not sufficient to influence the movement of VP7 from the ER to the Golgi apparatus. The only effect was to perturb the efficiency of glycosylation, perhaps for steric reasons, since the glycosylation site in the altered products is brought closer to the hydrophobic domains.