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

The herpes simplex virus (HSV) type 1 strict late (gamma) U(L)38 promo ter contains three cis-acting transcriptional elements: a TATA box, a specific initiator element, and the downstream activation sequence (DA S). DAS is located between positions +20 and +33 within the 5' untrans lated leader region and strongly influences transcript levels during p roductive infection. In this communication, we further characterize DA S and investigate its mechanism of action. DAS function has a strict s pacing requirement, and DAS contains an essential 6-bp core element, A similarly positioned element from the gamma gC gene (U(L)44) has part ial DAS function within the U(L)38 promoter context, and the promoter controlling expression of the gamma U(S)11 transcript contains an iden tically located element with functional and sequence similarity to U(L )38 DAS. These data suggest that downstream elements are a common feat ure of many HSV gamma promoters. Results with recombinant viruses cont aining modifications of the TATA box or initiator element of the U(L)3 8 promoter suggest that DAS functions to increase transcription initia tion and not the efficiency of transcription elongation. In vitro tran scription 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. Finall y, electrophoretic mobility shift assays and UV cross-linking experime nts 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 w ith DAS is required for efficient expression of U(L)38 and other HSV l ate genes.