TRANSACTIVATION OF ADENOVIRUS E2-EARLY PROMOTER BY E1A AND E4-6 7 IN THE CONTEXT OF VIRAL CHROMOSOME/

Transcription from adenovirus E2-early promoter is controlled by a uni que array of four cis-acting elements which include an atypical TBP si te, two E2F sites present in an inverted orientation relative to each other, and an ATF site. In virus-infected cells, this promoter is tran sactivated by E1A and the E4 6/7 proteins. In addition, it is also sti mulated by the DNA-binding protein (DBP) in transient transfection ass ays. Here we describe a genetic analysis of the E2 transcriptional reg ulation in the context of the viral chromosome. By using genetically e ngineered mutant adenoviruses we have determined the interrelationship between the different cis-acting elements of the E2-early promoter du ring basal transcription, the extent to which E1A and E4 6/7 contribut e to the E2 promoter activation and the E2 promoter elements that resp ond to these transactivators. We show that at eight hours following in fection, E1A can transactivate the promoter about 21-fold whereas E4 6 /7 can induce the promoter by only fivefold. DBP does not induce the p romoter in the chromosomal context. Our mutational analysis suggests t hat the unique architecture of the E2-early promoter necessitates the concerted interaction of all three host transcription factors with the ir cognate recognition elements to form a stable and functional transc ription complex. E1A mediated transactivation is dependent on this sta ble basal transcription complex and transactivation may involve simult aneous interaction of E1A with each of the three transcription factors present in the multicomponent basal transcription complex. The E4 6/7 protein can transactivate the E2-early promoter in the absence of ATF presumably by promoting the DNA binding capacity of transcription fac tor E2F and thereby stabilizing the basal transcription complex. We di scuss some of the possible protein-protein interactions that may take place at the level of the multicomponent transcriptional complex at th e E2-early promoter during transcriptional activation and the discrepa ncies that arise when a promoter is analyzed in infection versus trans fection assays. (C) 1996 Academic Press Limited