The E1b promoter of Ad12 in mouse L tk- cells is activated by adenovirus region E1a

We have investigated the effect of the E1a region of adenovirus on the expression of the E1b transcriptional unit in mouse L tk- cells. To that end we have fused the promoter region of the E1b gene of Ad12 to the coding sequence of the thymidine kinase gene of herpes simplex virus type 1. We found that expression of this fusion gene is completely dependent on the presence of the E1a region. Sequences involved in this regulation were mapped between positions -135 and +11 from the E1b cap site. In addition, we found that the largest E1a protein is essential in this regulation process.