The TATA homology and the mRNA 5' untranslated sequence are not required for expression of essential adenovirus E1A functions.

Adenovirus E1A encodes a protein that facilitates the transcription of other early viral transcriptional units and is required for virus-induced transformation. To study the function of non-protein-coding DNA sequence at the 5' end of this transcriptional unit, we constructed mutant viruses with deletions in this region. Deletion of sequence just upstream from the TATA homology does not affect the level or sequence of E1A mRNAs. Deletion of the TATA homology decreases the level of E1A mRNAs by a factor of 5-10 and shifts the mRNA 5' ends from the major 5' end found in wild-type transcripts to a set of minor ends found in wild-type E1A mRNAs. This suggests that the TATA homology is required for an efficient transcription initiation mechanism, and that in its absence a less efficient, less precise mechanism is unmasked. Analysis of mRNAs from other early regions establishes that E2 and E3 regions are most dependent on E1A functions for expression of maximal mRNA levels, E4 is less dependent and E1B is the least dependent. Deletion of the TATA homology, a sequence highly conserved among human adenoviruses, and the entire 5' untranslated sequence of the E1A mRNAs decreases neither the rate of virus replication in a host in which E1A expression is required, nor the efficiency of transformation of rat embryo cells.