Differentiation of the Shutoff of Protein Synthesis by Virion Host Shutoff and Mutant γ134.5 Genes of Herpes Simplex Virus 1

Abstract

vhsprotein is the product of the UL41 open reading frame of herpes simplex virus 1. The protein, made late in infection, is packaged into virions and, in newly infected cells, shuts off host protein synthesis by degrading mRNA. γ134.5 gene encodes a protein which precludes total shutoff of protein synthesis after the onset of viral DNA synthesis in infected cells of human derivation. The experiments reported here were designed to test the hypothesis that in cells infected with γ134.5−mutant the total shutoff of protein synthesis reflects the failure to alter the function ofvhsmade late in infection. Hence, double mutants,vhs−and γ134.5−should not cause total shutoff of protein synthesis. The mutants constructed to test the hypothesis were (i) viruses lacking 1 kbp from the coding domain of γ134.5 and carryinglacZ inserted into the coding domain of UL41, (ii) viruses with deletions in γ134.5 genes, (iii) viruses withlacZ inserted into UL41, and (iv) viruses in which the sequences of the deleted or interrupted genes were restored. We report that viruses with wild-type UL41 gene shut off the synthesis of actin, whereas viruses with interrupted genes made amounts of actin comparable to those of mock-infected cells. However, late in infection, protein synthesis in human neuroblastoma cells infected with the γ134.5−mutants was shut off irrespective of the status of the UL41 gene. Conversely, the phenotype of UL41−viruses with wild-type γ134.5 gene could not be differentiated from those of wild-type virus in the same assays. These studies indicate that the functions of the UL41 and γ134.5 genes and their products are independent of each other.