Expression of glycoprotein gIII-human decay-accelerating factor chimera on the bovine herpesvirus 1 virion via a glycosyl phosphatidylinositol-based membrane anchor.

Mutants of bovine herpesvirus 1 that express a truncated envelope glycoprotein gIII or a gIII-human decay-accelerating factor (hDAF) chimeric protein (gIII.hDAF) were employed to evaluate the function of the transmembrane and cytoplasmic domains of the gIII molecule. Truncated gIII (i.e., lacking the transmembrane and cytoplasmic region) was readily released from infected cells and was not detected on mature virus particles. In contrast, replacement of the transmembrane and cytoplasmic domains with the carboxyl-terminal portion of hDAF restored the expression of gIII on the membranes of infected cells as well as on virion surfaces. The presence of the gIII.hDAF chimera on virus particles was also associated with normal gIII function, i.e., the mediation of virus attachment and penetration. The gIII-hDAF chimera, which is present on both infected cell surfaces and virions, could be cleaved by a phosphatidylinositol-specific phospholipase C, indicating that it was anchored in the membrane via glycosyl phosphatidylinositol. Our results from this study suggest that the transmembrane and cytoplasmic regions of the gIII molecule serve as a general membrane anchor, but they do not contain structural signals required for the specific assembly of envelope proteins into mature virions.