THE HERPES-SIMPLEX VIRUS U(L)20 PROTEIN COMPENSATES FOR THE DIFFERENTIAL DISRUPTION OF EXOCYTOSIS OF VIRIONS AND VIRAL MEMBRANE-GLYCOPROTEINS ASSOCIATED WITH FRAGMENTATION OF THE GOLGI-APPARATUS

The Golgi apparatus is fragmented and dispersed in Vero cells but not in human 143TK(-) cells infected with wild-type herpes simplex virus 1. Moreover, a recombinant virus lacking the gene encoding the membrane proteid U(L)20 (U(L)20(-) virus) accumulates in the space between the inner and outer nuclear membranes of Vero cells but is exported and spreads from cell to cell in 143TK(-) cell cultures. Here we report that in Vero cells infected with U(L)20(-) virus, the virion envelope glycoproteins were of the immature type, whereas the viral glycoproteins associated with cell membranes were fully processed up to the addition of sialic acid, a trans-Golgi function. Moreover, the amounts of viral glycoproteins accumulating in the plasma membranes were considerably smaller than those detected on the surface of Vero cells infected with, wild-type virus. In contrast, the amounts of viral glycoproteins present on the plasma membranes of 143TK(-) cells infected with wild-type or U(L)20(-) virus were nearly identical. We conclude that (i) in Vero cells infected with U(L)20(-) virus the block in the export of virions is at the entry into the exocytic pathway, and a second block in the exocytosis of viral glycoproteins associated with cytoplasmic membranes is due to an impairment of transport beyond Golgi fragments containing trans-Golgi enzymes and not to a failure of the Golgi oligosaccharide-processing functions; (ii) these defects are manifested in cells in which the Golgi apparatus is fragmented; and (iii) the U(L)20 protein compensates for these defects by enabling transport to and from the fragmented Golgi apparatus.