Varicella-zoster Virus (VZV) Virion-associated Transactivator Open Reading Frame 62 Protein Enhances the Infectivity of VZV DNA

Varicella-zoster virus (VZV) open reading frame (ORF) 62 protein (the homolog of herpes simplex virus type 1 (HSV-1) ICP4) and ORF10 protein (the homolog of HSV-1 VP16) are virion-associated transactivators. To investigate whether these proteins function during the initial stages of VZV infection, human melanoma cells were cotransfected with purified VZV DNA, devoid of any structural proteins, along with a plasmid expressing VZV ORF62 or ORF10 under the control of the human cytomegalovirus major immediate-early promoter. Expression of ORF62 enhanced the infectivity of VZV DNA up to 70-fold. In contrast, expression of ORF10 enhanced the infectivity of VZV DNA only threefold. These results show that high-level expression of ORF62 protein increases the probability that transfected VZV DNA will result in productive infection, suggesting that this virion-associated transactivator (ORF62) has a critical role in initiating infection.