TRANSCRIPTIONAL ACTIVATION OF THE HERPES-SIMPLEX VIRUS TYPE-1 U(L)38 PROMOTER CONFERRED BY THE CIS-ACTING DOWNSTREAM ACTIVATION SEQUENCE IS MEDIATED BY A CELLULAR TRANSCRIPTION FACTOR

The herpes simplex virus (HSV) type 1 strict late (gamma) U(L)38 promoter contains three cis-acting transcriptional elements: a TATA box, a specific initiator element, and the downstream activation sequence (DAS). DAS is located between positions +20 and +33 within the 5' untranslated leader region and strongly influences transcript levels during productive infection. In this communication, we further characterize DAS and investigate its mechanism of action. DAS function has a strict spacing requirement, and DAS contains an essential 6-bp core element, A similarly positioned element from the gamma gC gene (U(L)44) has partial DAS function within the U(L)38 promoter context, and the promoter controlling expression of the gamma U(S)11 transcript contains an identically located element with functional and sequence similarity to U(L)38 DAS. These data suggest that downstream elements are a common feature of many HSV gamma promoters. Results with recombinant viruses containing modifications of the TATA box or initiator element of the U(L)38 promoter suggest that DAS functions to increase transcription initiation and not the efficiency of transcription elongation. In vitro transcription assays using uninfected HeLa nuclear extracts show that, as in productive infection with recombinant viruses, the deletion of DAS from the U(L)38 promoter dramatically decreases RNA expression. Finally, electrophoretic mobility shift assays and UV cross-linking experiments show that DAS DNA forms a specific, stable complex with a cellular protein (the DAS-binding factor) of approximately 35 kDa. These data strongly suggest that the interaction of cellular DAS-binding factor with DAS is required for efficient expression of U(L)38 and other HSV late genes.