The adenovirus type 5 E1A transcriptional control region contains a duplicated enhancer element

The adenovirus type 5 E1A transcriptional control region contains an element with enhancer properties located between -141 and -305 relative to the E1A cap site at +1. The enhancer element is located at or very close to a sequence required in cis for packaging of viral DNA. Deletion of the element reduces both the rate of transcription and steady-state levels of E1A mRNAs in virus-infected cells. Such deletions also cause a modest reduction in activity of the E1B transcription unit, which is located immediately downstream of the E1A unit. The enhancer element includes repeated core sequences. Function is retained when the element is moved to the 3' side of the E1A gene in either possible orientation, and the E1A enhancer functions in cis to enhance transformation by the herpesvirus thymidine kinase gene in both mouse and human cells.