Cell killing by viruses IV. Cell killing and protein synthesis inhibition by vesicular stomatitis virus require the same gene functions

Abstract

Temperature-sensitive (ts) mutants of vesicular stomatitis (VS) virus representing the five known complementation groups of the Indiana serotype were used to determine which viral gene functions were required for the expression of (i) cell-killing (CK) particle activity, and (ii) the inhibition of host cell protein synthesis. Cell-killing particle activity was quantitated by analyzing single-cell survival curves generated by infecting the Vero line of green monkey kidney cells at low multiplicities ( m pfp ≤ 5) and at permissive (30°) and nonpermissive (40°) temperatures. Cellular protein synthesis inhibition was measured by difference analysis of polyacrylamide-gel-electropherogram patterns obtained from uninfected mouse L cells and cells infected at high multiplicity ( m pfp = 100–500) at these two temperatures. Analyses of cell killing and protein synthesis inhibition by is mutants at nonpermissive temperature demonstrate that both of these attributes require the same viral gene functions and that they are conjointly expressed or not expressed, ts ckp +,psi + or ts ckp −,psi − , respectively. Complementation groups I and IV were subdivided into ts ckp +,psi + and ts ckp −,psi − mutants, establishing that the viral proteins required for the expression of cell killing and protein synthesis inhibition need not be fully functional. Considering these and previous results [ Virology 57: 321 1974; 63: 176 1975; 69: 378 1976] we conclude that, although the expression of both cell killing and protein synthesis inhibition by VS virus does not require infectious virus, it does depend upon transcription of viral genes N and NS by virion-associated transcriptase and their translation into minimally functional proteins. We postulate that viral proteins N and NS then interact with minimally functional L protein to produce the putative proximate or ultimate factor(s) directly responsible for cell killing and protein synthesis inhibition by VS virus. The lack of cellular protein synthesis inhibition by several is mutants following challenge at high multiplicities ( m pfp = 500) at 40° casts some doubt on the interpretation of experiments that appear to support assignment of these functions to preformed viral proteins.