Characterization of the early steps of herpes simplex virus replication in interferon-treated human cells

Interferon (IFN) was shown to inhibit herpes simplex virus type 1 (HSV-1) replication at the transcription of the immediate early (alpha) genes. This apparent inhibition could be due to a direct effect on viral transcription or on one of the preceding steps of infection, i.e., penetration and uncoating. In the present study, we analyze the effects of IFN on the very early steps of HSV-1 infection in HEp-2 human cells. Analysis of the parental HSV-1 viral DNA accumulated in the infected cell nuclei indicated that viral DNA penetration, migration to the nuclei, and stability were not affected by IFN treatment. To analyze the effect of IFN on the uncoating of the parental HSV-1 DNA following infection, we developed a technique based on DNase I sensitivity of the infecting viral DNA genome. Within 1 h of infection, the parental viral DNA became sensitive to DNase I digestion. HSV-1 DNA in the nuclei of both control and IFN-treated cells was equally sensitive to DNase I digestion, suggesting that IFN's mode of action was unrelated to the uncoating of HSV-1 virions. Because IFN does not affect the events in the HSV-1 lytic cycle prior to the onset of the immediate-early gene transcription, it appears that IFN exerts a direct effect on this process.