The Epstein-Barr virus (EBV) early promoter DR contains a cis-acting element responsive to the EBV transactivator EB1 and an enhancer with constitutive and inducible activities.

The Epstein-Barr Virus (EBV) DR promoter controlled the expression of the PstI repeat region IR4. This promoter was activated by the EBV trans-acting factor EB1, mainly at the transcriptional level, and the activation was mediated by the TATA box and two cis-acting regulatory regions, one proximal to the TATA box and one distal to the TATA box. The distal region had enhancer properties. In HeLa cells, it activated transcription from the herpes simplex virus type 1 thymidine kinase promoter linked to the chloramphenicol acetyltransferase gene when located in inverted orientation upstream of the thymidine kinase promoter or downstream of the chloramphenicol acetyltransferase gene coding sequence. This enhancer also activated transcription from the simian virus 40 early upstream regulatory elements. These results indicate that the DR These results indicate that the DR enhancer can constitutively activate heterologous promoters in HeLa cells. However, the DR enhancer was not active in EBV genome-negative B cell lines, but it became active when these cells were infected by EBV and when the expression of the EBV early genes was induced by EB1. This suggests that an EBV early gene product induces the DR enhancer activity. The DR promoter TATA box-proximal cis-acting regulatory element contained EB1-responsive sequences.