The mammalian activator protein ATF stimulates transcription from the adenovirus E4 promoter by binding to multiple upstream promoter and enhancer elements. DNAase footprint analyses have revealed that there are cooperative interactions between ATF and TFIID (the mammalian TATA factor) when both are bound simultaneously to the promoter and that these interactions in turn facilitate promoter recognition by RNA polymerase II and the general initiation factors TFIIB and TFIIE. However, the complex of TFIID and the other general factors is stable following oligonucleotide-mediated dissociation of ATF from the complete preinitiation complex. These results indicate that TFIID is a direct target for ATF, that these interactions facilitate assembly of a complete preinitiation complex, and that the role of ATF might be transient.