FIG. 4.

The VZV gene 21 promoter is silent in uninfected cells. The 284-bp VZV DNA segment separating ORFs 20 and 21 was inserted into the CAT reporter plasmid and used to transfect either uninfected cells (lane 2) or VZV-infected cells (lane 4). Controls included the CAT reporter plasmid lacking a promoter transfected into uninfected cells (lane 1) or VZV-infected cells (lane 3) and a CMV IE promoter driving CAT transfected into uninfected cells (lane 5). CAT assays were performed in duplicate, and the average acetylation of chloramphenicol (%CAT) showed that the VZV gene 21 promoter does not function in uninfected cells (−VZV) but is active in VZV-infected cells (+VZV). The amount of promoter activity in infected cells above that in uninfected cells (fold) showed that gene 21 promoter activity was approximately 650-fold higher in VZV-infected cells than in uninfected cells.