Differentiation of the shutoff of protein synthesis by virion host shutoff and mutant γ134.5 genes of herpes simplex virus 1

Abstract

vhs protein is the product of the U(L)41 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 of vhs made 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 carrying lacZ inserted into the coding domain of U(L)41, (ii) viruses with deletions in γ134.5 genes, (iii) viruses with lacZ inserted into U(L)41, and (iv) viruses in which the sequences of the deleted or interrupted genes were restored. We report that viruses with wild-type U(L)41 gene shutoff 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 shutoff irrespective of the status of the U(L)41 gene. Conversely, the phenotype of U(L)41 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 U(L)41 and γ134.5 genes and their products are independent of each other.