The human adenovirus E1A 243 amino acid oncoprotein possesses a transcription repression function that appears to be linked with its ability to induce cell cycle progression and to inhibit cell differentiation. The molecular mechanism of E1A repression has been poorly understood. Recently, we reported that the TATA binding protein (TBP) is a cellular target of E1A repression. Here we demonstrate that the interaction between TBP and the E1A repression domain is direct and specific. The TBP binding domain within E1A 243R maps to E1A N-terminal residues ϳ1 to 35 and is distinct from the TBP binding domain within conserved region 3 unique to the E1A 289R transactivator. An E1A protein fragment consisting of only the E1A N-terminal 80 amino acids (E1A 1-80) and containing the E1A repression function was found to block the interaction between TBP and the TATA box element as shown by gel mobility and DNase protection analysis. Interestingly, a preformed TBP-TATA box promoter complex can be dissociated by E1A 1-80. Further, TFIIB can prevent E1A disruption of TBP-TATA box interaction. TFIIB, like TBP, can overcome E1A repression of transcription in vitro. The ability of the E1A repression domain to block TBP interaction with the TATA box and the ability of TFIIB to reverse E1A disruption of the TBP-TATA box complex implies a mechanism for E1A repression distinct from those of known cellular repressors that target TBP.Adenovirus (Ad) encodes two major regulatory proteins of 243 and 289 amino acid residues (E1A 243R and E1A 289R for group C Ads) synthesized from alternatively spliced RNA transcripts of 12S and 13S encoded by early region E1A. E1A proteins contain multiple independent domains involved in diverse functions, including transcriptional activation, transcriptional repression, induction of cellular DNA synthesis, cell immortalization, and cell transformation as well as inhibition of metastasis and cell differentiation (for reviews, see references 9, 13, 43, and 47). E1A 289R differs from E1A 243R by conserved region 3 (CR3), a 46-amino-acid domain unique to 289R (see Fig. 1 for location of conserved regions). CR3 is essential (18,26,33,41,46) and sufficient (20, 34) for activation of viral early genes. Domains common to E1A 243R and 289R are required for the growth-regulatory functions of E1A; these include the relatively nonconserved N terminus (amino acid residues 1 to 39), CR1 (residues 40 to 80), and CR2 (residues 120 to 139) (40).Ad E1A 243R is a potent inducer of cellular DNA synthesis and a strong deregulator of cell cycle control. Two separate domains of E1A 243R can induce progression of quiescent cells to S-phase cellular DNA synthesis by independent pathways (24, 34). The first pathway involves binding sites within CR1 and CR2 for the retinoblastoma tumor suppressor protein, pRb. These sites sequester and dissociate pRb and related family members from complexes with the E2F family of transcription factors, whose activities can induce cell cycle progression (for a review, see reference 44). The second ...

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Early gene E5 of bovine papillomavirus type 1 encodes a 44-amino-acid protein whose expression can transform immortalized mouse cell lines. We have previously reported that a chemically synthesized ES peptide functions to induce cellular DNA synthesis upon microinjection into growth-arrested mouse cells. We further defined the two E5 domains essential for the full DNA synthesis induction activity by the analysis of E5 deletion and amino acid substitution mutant peptides. The first domain is the C-terminal 13-amino-acid core which is sufficient to activate DNA synthesis at high peptide concentration and contains two essential, highly conserved cysteine residues. The second domain is the 7-amino-acid hydrophobic sequence contiguous to the core domain which is sufficient to confer a 1,000-fold higher molar specific activity to the E5 peptide. A random hydrophobic sequence, but not charged amino acids, fulfills the function of the second domain.

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