Variable requirements for herpes simplex virus immediate-early proteins in the expression of the adenovirus E2 gene

Regulation of the adenovirus E2 gene by trans-activating proteins encoded by herpes simplex virus was investigated. Coinfection of Vero cells was performed with Ad5 dl312 (an E1 deletion mutant) and either wildtype HSV, mutant virus encoding a temperature-sensitive ICP4 protein (tsK), or mutants carrying deletions in the ICP4 (d120) or ICP0 (dl x 3.1) gene. As detected by the presence of E2 mRNA, or the product of the E2 gene, 72-kDa DNA binding protein (DBP), functional ICP4 was sufficient for expression of the E2 gene. Regulation of E2 gene expression was at the level of transcription activation as judged by nuclear run-on assay. In contrast to results when Vero cells were coinfected, expression of 72-kDa DBP in CN3 cells, carrying an integrated copy of the E2 gene, required expression of both HSV immediate-early proteins. These results suggest that the DNA-protein organization of the target gene sequence may play a significant role in the ability of viral regulatory proteins to activate expression of heterologous as well as homologous genes.