Mapping of Herpes Simplex Virus-1 Neurovirulence to γ ₁ 34.5, a Gene Nonessential for Growth in Culture

TLDR

The HSV‑1 γ1 34.5 gene, located in inverted repeats and present in two copies, is not required for viral replication in cell culture. The authors constructed four recombinant HSV‑1 strains: a double‑gene deletion, a double‑stop‑codon mutant, an epitope‑tagged version, and a revertant restoring the deleted sequences. Deletion or stop‑codon mutants were avirulent in mice, whereas the epitope‑tagged virus retained moderate virulence and the revertant restored full virulence, confirming that γ1 34.5 is essential for neurovirulence by permitting replication and destruction of brain cells.

Abstract

The gene designated γ 1 34.5 maps in the inverted repeats flanking the long unique sequence of herpes simplex virus-1 (HSV-1) DNA, and therefore it is present in two copies per genome. This gene is not essential for viral growth in cell culture. Four recombinant viruses were genetically engineered to test the function of this gene. These were (i) a virus from which both copies of the gene were deleted, (ii) a virus containing a stop codon in both copies of the gene, (iii) a virus containing after the first codon an insert encoding a 16-amino acid epitope known to react with a specific monoclonal antibody, and (iv) a virus in which the deleted sequences were restored. The viruses from which the gene was deleted or which carried stop codons were avirulent on intracerebral inoculation of mice. The virus with the gene tagged by the sequence encoding the epitope was moderately virulent, whereas the restored virus reacquired the phenotype of the parent virus. Significant amounts of virus were recovered only from brains of animals inoculated with virulent viruses. Inasmuch as the product of the γ 1 34.5 gene extended the host range of the virus by enabling it to replicate and destroy brain cells, it is a viral neurovirulence factor.