An adenovirus E1A protein domain activates transcription in vivo and in vitro in the absence of protein synthesis.

We have shown previously that a synthetic peptide of 49 amino acids, encoding mainly adenovirus E1A protein domain 3 (PD3), functions as an autonomous transcriptional activator. Here we provide two lines of evidence showing that E1A transactivation does not require the induction of cellular protein synthesis. First, PD3 rapidly transactivates E1A-inducible early viral genes in the presence of inhibitors of protein synthesis, as demonstrated by microinjection-in situ hybridization experiments. Second, PD3 greatly stimulates transcription of E1A-inducible genes in vitro. Mutant PD3 peptides with single amino acid substitutions in conserved cysteine residues are defective in transactivation both in vivo and in vitro. Our findings provide compelling evidence that protein synthesis is not required for E1A transactivation, and support a model in which E1A modifies the activity of a preexisting cellular protein(s) involved in the regulation of transcription.