A genetic test for expression of a functional herpes simplex virus DNA-binding protein from a transfected plasmid.

The major DNA-binding protein, ICP8, encoded by herpes simplex virus is localized to the infected cell nucleus where it plays a role in viral DNA replication and control of viral gene expression. To identify the parts of the ICP8 protein that are important for its localization and functions, we have developed a system to test the ability of recombinant plasmids to express functional ICP8. A recombinant plasmid containing the wild-type ICP8 gene was transfected into cells. The cells were later infected with a temperature-sensitive ICP8 mutant virus at the nonpermissive temperature. Sufficient wild-type ICP8 was expressed from the transfected plasmid to complement the replication of the mutant virus. This provides a genetic system to test the properties of ICP8 expressed from mutagenized plasmids without the establishment of a stable cell line or the reintroduction of the ICP8 gene into the herpes simplex virus genome.