ROLE OF THE DR2 REPEAT ARRAY IN THE REGULATION OF THE ICP34.5 GENE PROMOTER OF HERPES-SIMPLEX VIRUS TYPE-1 DURING PRODUCTIVE INFECTION

Previous analyses using transient transfection assays indicated that t he promoter for the gene encoding the herpes simplex virus type 1 (HSV -1) neurovirulence protein ICP34.5 can be divided into an essential co re region of approximately 80 bp and two potent upstream silencer doma ins corresponding to the DR2 and DR6 repeat arrays, In order to examin e the potential role of transcriptional silencing during productive HS V-1 infection, recombinant viruses were generated in which wild-type o r mutant ICP34.5 promoters controlling the expression of a chloramphen icol acetyltransferase reporter gene were inserted into the thymidine kinase gene of the viral genome. The intact promoter in the virus HSV- Delta 1CAT exhibited delayed-early kinetics of expression that were co mparable to those of the ICP34.5 gene promoter at its native site in t he genome, Deletion of the core promoter domain eliminated promoter ac tivity in the virus HSV-Delta 5CAT, indicating that this region was re quired for expression not only in transient transfections assays but a lso in the context of the viral genome. However, deletion of the DR2 r epeat array from the ICP34.5 promoter in the virus HSV-Delta 7CAT was found to increase promoter activity only minimally at late times, and even to reduce activity at early times. Thus, in marked contrast to it s behaviour in transient expression assays, the DR2 repeat array does not appear to act as a transcriptional silencer in the context of the HSV-1 genome during productive infection.