Promoter sequence and cell type can dramatically affect the efficiency of transcriptional activation induced by herpes simplex virus type 1 and its immediate-early gene products Vmw175 and Vmw110.

The activation of transcription of the early and late classes of viral genes during infection by herpes simplex virus type 1 (HSV-1) requires the prior expression of immediate-early (IE) gene products. The IE gene products can also activate certain cellular and heterologous viral promoters. This paper presents a thorough analysis of transactivation of the HSV-1 glycoprotein gD and simian virus 40 early promoters, and two other promoters that are hybrids of both, under a variety of experimental conditions. Two methods of transactivation (superinfection with virus and co-transfection with isolated IE genes) have been used with all four target promoters in a variety of cell types. The conclusions are: (1) promoter sequence affects the efficiency of promoter activation by infectious HSV-1 virus, but this activation is not restricted to HSV promoters; (2) cell type affects the efficiency of promoter activation by HSV-1, and this can lead to a failure to activate a promoter in one cell type but not in others in which activation is generally more efficient; (3) a promoter can be activated to different extents in co-transfection experiments using plasmids carrying isolated IE genes that express Vmw110 or Vmw175 or when both are used together; (4) the pattern of activation of a promoter by the IE gene products in cotransfection experiments varies in different cell types; (5) changes in promoter sequence can alter the pattern of activation by the different IE polypeptides, and this pattern can again differ in different cell types; (6) other apparently minor experimental variables, as might exist between the standard methods used in different laboratories, can also affect the patterns of activation observed. The results are discussed in terms of the mechanism of action of the HSV-1 IE gene products and the limitations of the co-transfection assay.