Sequence-specific activation of transcription by adenovirus EIa products is observed in HeLa cells but not in 293 cells

Activation of the adenovirus-2 E2a late promoter during inhibition of protein synthesis by cycloheximide

The 5' termini of human adenovirus 2 (Ad2) E2a mRNA, which starts at two separate (early and late) promoter regions, were mapped on Ad2 nucleotide sequences with the aid of primer extension analysis and quantitated. In the early stage (6 h) of Ad2 infection of KB cells and 293 cells, E2a mRNA started mostly at the early (75.4 mp) promoter region. When these infected cells were cultured in the presence of cycloheximide from 1 to 6 h postinfection, the transcription from the late (72.2 mp) promoter region increased. Especially in 293 cells, approx. 50% of E2a mRNA started at the late promoter region. We conclude from the results that the activation of the late promoter during infection does not depend on viral DNA replication. Our results suggest the involvement of cellular protein(s) in this activation.

Functional domains of adenovirus type 5 E1a proteins

Adenovirus E1a proteins function in transcriptional activation, transcriptional repression, cellular DNA synthesis induction, and cellular transformation. Here we examine the role of the previously undefined E1a region 1, the last of three conserved E1a regions to be characterized. Region 1 is required for transcriptional repression, transformation, and DNA synthesis induction, but not transcriptional activation. These results support our previous suggestion that transcriptional repression is the basis of E1a-mediated transformation. Two conserved regions (regions 1 and 2), present in both early E1a proteins, are essential for transcriptional repression, transformation, and induction of DNA synthesis. In contrast, mutagenesis suggests that transcriptional activation requires only 49 amino acids (region 3) unique to the 289 amino acid E1a protein. This we prove by demonstrating that a 49 amino acid region 3 synthetic peptide efficiently activates an E1a-inducible promoter. This peptide is the smallest known protein fragment functioning as a transcriptional activator.

E1a inducibility of the adenoviral early E2a promoter is determined by specific combinations of sequence elements

By transient expression analysis in HeLa cells of adenovirus-2 E2a early (E2aE) promoter mutants and hybrid E2aE-beta-globin gene constructs, we demonstrate the existence of three nucleotide (nt) sequence elements involved in the E1a-responsiveness of the E2aE transcription unit: element I, localized within a segment (nt -13 to +62) surrounding the major E2aE cap site (nt + 1); element II (between nt -71 and -29), and element III (between nt -146 and -86). Each element is unable by itself to confer E1a responsiveness. Only combinations of sequences including elements I and II (spanning nt -71 and +62) or II and III (spanning nt -146 and -29) ensure maximal inducibility, for which element II appears of central importance.