The initiator directs the assembly of a transcription factor IID-dependent transcription complex.

Highly purified RNA polymerase II was found to be able to weakly recognize the initiator (Inr) present in the adenovirus IVa2 and major late promoters. The association of RNA polymerase II with the Inr was enhanced by the general transcription factors. The Inr was capable of directing the formation of a DNA-protein complex. Transcription competent complexes on the adenovirus major late and IVa2 promoters appear to be formed by alternative pathways mediated through the Inr and/or "TATA" motif. The presence of both motifs, however, is required for efficient transcription utilizing a discrete start site. Complexes formed at either site required transcription factor TFIID, the TATA binding protein. Consistent with this observation, a TFIID requirement was demonstrated for transcription from a mutant adenovirus major late promoter construct lacking a functional TATA motif.