AN ANALYSIS OF THE IN-VITRO AND IN WHO PHENOTYPES OF MUTANTS OF HERPES-SIMPLEX VIRUS TYPE-1 LACKING GLYCOPROTEINS GG, GE, GI OR THE PUTATIVE GJ

Mutants of herpes simplex virus type 1 (HSV-I) lacking glycoproteins g G, gE, gI or the putative gJ were constructed by inserting a lacZ expr ession cassette within the US4, US8, US7 and US5 genes respectively. R evertant viruses were then constructed by rescue with a wild-type DNA fragment. Each of these mutant viruses, by comparison with the parenta l virus HSV-1 SC16, exhibited normal particle to infectivity ratios, a nd had no discernible phenotypic abnormalities in baby hamster kidney- 21 cells following high or low multiplicity infections. Infection of m ice by scarification of the ear with these mutant viruses showed the f ollowing. (i) Interruption of the US5 (gJ) gene has no effect on the a bility of HSV-1 to multiply at the inoculation site or its ability to enter or multiply in the peripheral or central nervous system (CNS). T his shows that the US5 gene provides a convenient site for the inserti on of foreign genes for both in vitro and in vivo studies. (ii) Disrup tion of the US4 (gG) gene results in marginal attenuation in the mouse ear model. (iii) Disruption of the US7 (gI) or US8 (gE) genes results in pronounced attenuation; virus was rapidly cleared from the inocula tion site and was barely detectable in sensory ganglia or in the CNS. The failure of gI-negative or gE-negative viruses to replicate efficie ntly at the inoculation site in vivo led to the investigation of virus behaviour in epithelial cells in vitro. Viruses lacking gE or gI adso rbed to and entered these cells at normal rates compared with the pare ntal virus, but formed minute plaques. This is consistent with a failu re of cell-to-cell spread by the cell contact route. This was confirme d by measurement of the rate of increase in infectious centre numbers following low multiplicity infections. The view that gE and gI influen ce interactions between cells at the plasma membrane was reinforced by showing that the introduction of disrupted gE or gI genes into a sync ytial, but otherwise syngeneic, background resulted in a non-syncytial phenotype. We conclude that the gE-gI complex plays a part, at least in some cell types, in the interactions at the cell surface that allow transmission of the virus from infected to uninfected cells by cell c ontact. In syncytial strains this leads to uncontrolled membrane fusio n. The observation that virions lacking gE or gI enter cells at appare ntly normal rates reinforces the view that cell-cell fusion is not ana logous to the fusion of the virion envelope with the plasma membrane f or nucleocapsid entry. It is also apparent that the phenotypes of HSV- 1 mutants lacking gI or gE are similar in many respects to those repor ted for mutants of pseudorabies virus lacking the gE homologue.