Far upstream initiation sites for adenovirus early region 1A transcription are utilized after the onset of viral DNA replication.

Adenovirus early region 1A (E1A) is the first transcription unit expressed after infection. It encodes a protein which controls the expression of all other early viral genes. The E1A mRNAs have one major capped 5' terminus which maps 31 nucleotides downstream from a T-A-T-A sequence (C. Baker and E. Ziff. J. Mol. Biol. 149:189-221, 1981). In addition, a minor set of E1A mRNAs are observed during the early phase of infection which have 5' termini mapping at approximately -160, -185, and -230 relative to the major cap site (Osborne et al., Cell 29:139-148, 1982). Here we report the occurrence of another set of minor E1A mRNAs which were observed exclusively after the initiation of viral DNA replication. These late specific E1A mRNAs had cap sites which mapped at approximately -300, -325, -360, and -375 relative to the major cap site. The appearance of these minor late E1A mRNAs was blocked by the DNA synthesis inhibitor cytosine arabinoside. These same late specific E1A mRNAs were synthesized from E1A-containing plasmids which replicate in monkey cells. This demonstrated that neither late specific adenovirus proteins nor adenovirus-specific chromatin structure was required for the production of the late specific E1A mRNAs. Adenovirus mutants in which the E1A T-A-T-A box region had been deleted also synthesized the corresponding deleted forms of the late specific mRNAs after initiation of DNA replication. These results indicate that the process of DNA replication alters the specificity of E1A transcription initiation in a promoter region which is at least 375 nucleotides in length.