Deletion of the virion host shut-off gene of pseudorabies virus results in selective upregulation of the expression of early viral genes in the late stage of infection

A real-time RT-PCR technique was applied to evaluate the impact of deletion of the virion host shut-off (VHS) gene on the kinetics of pseudorabies virus gene expression. Selective suppression of early gene transcripts by the viral ribonuclease occurs after 4 h of infection; while VHS protein appears to act non-selectively on the transcripts belonging in different kinetic classes in the first 2 h of infection. VHS protein disrupts the close correlation between the transcription kinetics of the immediate-early 180 protein and the other pseudorabies virus transcripts. The typical pattern of early gene expression was found to be altered in the VHS gene-deleted virus in that the production rates of their transcripts did not decline from 4 h post-infection. This observation led us to put forward the hypothesis that the VHS protein may play a pivotal role in the switch from the early to the late stage of infection.