Adenovirus E1a Proteins Repress Transcription from the SV40 Early Promoter

Using a transient expression assay in HeLa cells, we show that products from the adenovirus-5 E1a transcription unit repress transcription from the SV40 early promoter. The repression is unrelated to T antigen autoregulation, occurs maximally with low concentrations of E1a expression plasmid, is exerted at the transcriptional level, and requires functional E1a protein. The 289 and 243 amino acid E1a proteins are equally effective at repressing transcription. Since only the 289 amino acid protein is efficient at activating transcription, we conclude that activation and repression are separate E1a functions. We discuss possible mechanisms for E1a repression and the relationship of repression to the function of E1a in cell immortalization and transformation.