Differential regulation by varicella-zoster virus (VZV) and herpes simplex virus type-1 trans-activating genes

Transient expression assays were performed in Vero cells in order to compare varicella-zoster virus (VZV)-encoded trans-activating proteins [defined by the products of open reading frames (ORF) 4 and 62] with herpes simplex virus type-1 (HSV-1) trans-activating proteins, ICP4 and ICP0, with respect to activation of gene expression. We demonstrate that the product of VZV ORF4 and ORF62 (which are the HSV-1 analogs of ICP27 and ICP4, respectively) stimulate a variety of viral and cellular gene promoters, including the HSV-1 thymidine kinase (tk) promoter. On the other hand, expression of a recombinant vector containing the VZV tk promoter could not be stimulated, by HSV-1 infection or by the HSV-1 ICP4 or ICP0 proteins expressed during cotransfection experiments. These data suggest different mechanisms of activation of the VZV and the HSV-1 tk gene promoters by "trans-activating" factors.