COMPARISON OF THE EFFECTS OF SINDBIS VIRUS AND SINDBIS VIRUS REPLICONS ON HOST-CELL PROTEIN-SYNTHESIS AND CYTOPATHOGENICITY IN BHK CELLS

Infection of BHK cells by Sindbis virus leads to rapid inhibition of h ost cell protein synthesis and cytopathic effects (CPE). We have been studying these events to determine whether the expression of a specifi c viral gene is required and, in the present study, have focused our a ttention on the role of the structural proteins-the capsid protein and the two membrane glycoproteins. We tested a variety of Sindbis viruse s and Sindbis virus replicons (virus particles containing an RNA that is self-replicating but,vith some or all of the viral structural prote in genes deleted) for their abilities to inhibit host cell protein syn thesis and cause CPE in infected BHK cells. Our results show that shut off of host cell protein synthesis occurred in infected BHK cells when no viral structural proteins were synthesized and also under conditio ns in which the level of the viral subgenomic RNA was too low to be de tected. These results support the conclusion that the early steps in v iral gene expression are the ones required for the inhibition of host cell protein synthesis in BHK cells. In contrast, the Sindbis viruses and Sindbis virus replicons were clearly distinguished by the time at which CPE became evident. Viruses that synthesized high levels of the two membrane glycoproteins on the surface of the infected cells caused a rapid (12 to 16 h postinfection) appearance of CPE, and those that did not synthesize the glycoprotein spikes showed delayed (30 to 40 h) CPE.