CONSTRUCTION AND CHARACTERIZATION OF A STABLY TRANSFORMED HELA-CELL LINE IN WHICH THE EXPRESSION OF BOVINE HERPESVIRUS-1 ICP0 (BICP0) IS INDUCED BY TETRACYCLINE

To explore the effects BICP0 (a principal transactivator of BHV-1 gene expression) on viral promoter elements, we established a cell line in which the expression of BICP0 is regulated by tetracycline. A hybrid promoter containing reiterated copies of the tet-operator (tet-O) and a minimal herpesviral alpha gene transinducing factor (alpha TIF) resp onsive element (minimal human cytomegalovirus immediate early promoter ) was fused to the BICP0 gene and used to transform a HeLa cell line w hich expressed a fusion protein consisting of the repressor of the tet -O and the transactivating domain of alpha TIF. Simultaneously, the hy gromycin resistance gene was transfected to select cells in media cont aining either hygromycin alone or both hygromycin and tetracycline. Im munofluorescent assays indicated that BICP0 was synthesised in the tra nsformed cell lines solely upon induction of the gene by tetracycline removal. Only cells which had been kept constantly in medium containin g tetracycline were able to synthesise BICP0 upon induction. Induced c ell lines transactivated the native BICP0 promoter as well as the herp es simplex virus thymidine kinase promoter and the long terminal repea t sequences of human immunodeficiency virus in a dose dependent manner . These cell lines may help to further explore the functions of BICP0 as well as to investigate the molecular basis of interactions between herpes-and retroviruses.