Activation of transcription of the human cytomegalovirus early UL4 promoter by the Ets transcription factor binding element

The human cytomegalovirus (HCMV) early UL4 promoter has served as a useful model for studying the activation of early viral gene expression. Previous transient-transfection experiments detected cis-acting elements (the NF-Y s ite and site 2) upstream of the transcriptional start site (L. Huang and M. F. Stinski, J. Virol. 69:7612-7621, 1995). The roles of two of these sites , the NF-Y site and site 2, in the context of the viral genome were investi gated further by comparing mRNA levels from the early UL4 promoter in human foreskin fibroblasts infected by recombinant viruses with either wild-type or mutant cis-acting elements. Steady-state mRNA levels from the UL4 promo ter with a mutation in the NF-Y site were comparable to that of wild type. A mutation in an Elk-l site plus putative IE86 protein binding sites decrea sed the steady-state mRNA levels compared to the wild type at early times a fter infection. Electrophoretic mobility shift assays and antibody supershi fts detected the binding of cellular transcription factor Elk-l to site 2 D NA with infected nuclear extracts but not with mock-infected nuclear extrac ts. The role of cellular transcription factors activated by the mitogen act ivated protein kinase/extracellular signal-regulated kinase pathway in acti vating transcription from early viral promoters is discussed.