A herpes simplex virus mutant in which glycoprotein D sequences are replaced by β-galactosidase sequences binds to but is unable to penetrate into cells

Herpes simplex virus (HSV) glycoprotein gD is a major component of the virion envelope and is thought to play an important role in the initial stages of viral infection and stimulates the production of high titers of neutralizing antibodies. We assumed that gD plays an essential role in virus replication, and so to complement viruses with mutations in the gD gene we constructed a cell line, denoted VD60, which is capable of expressing high levels of gD after infection with HSV. A recombinant virus, designated F-gDβ in which sequences encoding gD and a nonessential glycoprotein, gI, were replaced by Escherichia coli β-galactosidase sequences, was selected on the basis that it produced blue plaques on VD60 cell monolayers under agarose overlays containing 5-bromo-4-chloro-3-indolyl-β-D-galactopyranoside (X-Gal). F-gDβ was able to replicate normally on complementing VD60 cells. However, F-gDβ was unable to form plaques on noncomplementing Vero cells. Virions lacking gD were produced in normal amounts by Vero cells infected with F-gDβ, and the virus particles were distributed throughout the cytoplasm and on the cell surface, suggesting that gD is not essential for HSV envelopment and egress. Virions lacking gD were able to bind to cells, but were unable to initiate synthesis of viral early polypeptides. Plaque production of F-gDβ particles lacking gD was enhanced by polyethylene glycol treatment, suggesting that gD is essential for penetration of HSV into cells. Other HSV glycoproteins have been implicated in the entry of virus into cells, and thus this process appears to involve multiple interactions at the cell surface.