Mapping of the bovine herpesvirus 1 glycoprotein C promoter region and its specific transactivation by the viral BICP27 gene product.

We investigated the cis-acting sequences of the promoter regulating the gene encoding the glycoprotein C (gC) of bovine herpesvirus 1 (BoHV-1), a gene of the gamma1 class. S1 nuclease protection assays revealed that gC transcription initiated predominantly at position C18281 of the viral genome, corresponding to 21 and 56 bases downstream from putative TATA-like and CAAT boxes, respectively. To map the gC promoter (pgC), we measured the ability of a series of nested deletions of the region +71 to -1155 with respect to the major gC transcriptional start site, to drive expression of the firefly luciferase (Luc) reporter gene following transient transfection of a cell host, in the absence as well as in the presence of viral factors expressed in trans. We show that the minimal pgC sequences required to drive maximal BoHV-1 independent expression was within the region +71 to -76 which harbours the putative TATA and CAAT boxes, the mRNA start site, and the complete 5' transcript leader sequence. This small pgC fragment was highly trans-activated by the co-expression of the BoHV-1-encoded BICP27 protein, but not BICP0 nor BTIF. In contrast, the pgC fragment spanning the region +71 to -1155 was only minimally trans-activated by BICP27, but substantially stimulated by BICP0. These findings thus suggest that gC gene regulation may involve the combined action of several viral transactivators.