Effect of polylysine on the early stages of infection of wild type pseudorabies virus and of mutants defective in gIII

The main pathway of adsorption of pseudorabies virus (PrV) to its host cells is via interactions between viral glycoprotein gIII and a cellular heparin-like receptor. Mutants of PrV deficient in glycoprotein gill adsorb by an alternative, slower pathway. Penetration into the cells of gIll− mutants is also delayed compared to penetration of wild type virus. We show here that polylysine enhances the adsorption of gill- mutants. Furthermore, in the presence of polylysine the adsorption of wild type virus involving the interactions of viral glycoprotein gill and the heparin-like cellular receptor is efficiently bypassed. Polylysine appears to promote virus adsorption by bridging the cellular and viral membranes. Polylysine not only stimulates adsorption of gIII− mutants but also promotes their internalization; the delay in the initiation of viral protein synthesis that is observed in cells infected with gIII− mutants compared to wild type infected cells is abrogated. Because it is unlikely that polylysine can substitute for two different functions of gIII, adsorption and penetration, the delay in the initiation of the infectious cycle in gIII−-infected cells is probably related to the defect in adsorption. Furthermore, polylysine can completely overcome the inhibitory effects of antisera against gIII, but not the inhibitory effects of antisera that affect a later stage of infection. It is unlikely therefore that polylysine can promote penetration directly and that gIII is involved directly in penetration. These results, as well as those obtained previously, show that while gill is essential for the efficient adsorption of PrV, it affects virus penetration only indirectly.