The adenovirus-2 early EIIa transcription unit possesses two overlapping promoters with different sequence...

The EIa-inducible, EIIa transcription unit of adenovirus-2 is transcribed early in infection from two start sites (+1 or EIIaE1 and -26 or EIIaE2), neither of which is preceded by canonical TATA box elements. Analysis of promoter deletion and linker scanning mutations for in vivo transcriptional activity after transfection into HeLa cells has indicated the existence of two overlapping promoters in the EIIaE gene. Two regions, each approximately 30 nucleotides upstream from start sites EIIaE1 and EIIaE2, function as TATA box substitutes. A sequence centered at position -42 (with respect to the major start site at position +1) is essential for transcription from both sites, while an element further upstream, localized between nucleotides -91 and -62, is also required for efficient EIIaE transcription, with the 3' border being dispensable for EIIaE2 transcription. Analysis of the entire series of EIIaE mutants, co-transfected with an EIa-containing plasmid, revealed that no unique sequence elements in the EIIaE1 promoter region between -97 and +1 were responsible for the stimulation of EIIaE1 transcription by EIa. In contrast, the EIa-mediated augmentation of EIIaE2 template activity was mainly dependent upon a sequence, the 5'-TTAAATTT-3' putative TATA box substitute, located around position -59.