Characterization of Factors Affecting the Virion Host Shutoff Function of Herpes Simplex Virus

Abstract

Herpes Simplex virus (HSV) virions contain the protein vhs (virion host shutoff), which is known to trigger rapid shutoff of host protein synthesis and accelerated decay of viral and cellular mRNAs. HSV-1 strains generally cause weaker shutoff than HSV-2 strains. HSV viruses lacking the VP16 viral transactivator gene show uncontrolled shutoff late in infection (Lam et al., 1996); vhs is known to bind to VP16 (Smibert et al., 1994). In vitro experiments demonstrated that HSV-1 vhs protein (vhsTl) and an intertypic HSV-2 G vhs protein (vhsT2) did not differ in ability to effect mRNA degradation in a rabbit reticulocyte lysate (RRL) assay system, suggesting that virion factors might influence vhs shutoff phenotype. To investigate the possibility that VP 16 influences early shutoff during HSV infection, a virus was constructed containing the HSV-2 strain G VP16 in place of HSV-1 VP16. This virus (8MA2R) grew in a noncomplementing cell line and was unaltered in shutoff phenotype compared to wt strain. Cotransfection assays demonstrated vhsT2 had greater shutoff ability than vhsT1, and this was confirmed in a viral system by constructing intertypic viruses containing portions of the HSV-2 G vhs ORF in a vhs-null HSV-1 tk locus. All intertypic constructs conferred increased shutoff ability relative to vhsT 1, indicating that the strong shutoff ability of HSV -2 vhs is distributed along much of the vhs ORF. Also, to confirm the observation that UL13 null viruses show a lack of shutoff which is not due to lack of vhs in the virion (Overton et al., 1994) a number of wildtype viruses and their UL13-null derivatives were tested for ability to shutoff host translation. All showed near-wt or wt levels of shutoff.