Conserved TAAAT motif in vaccinia virus late promoters: overlapping TATA box and site of transcription initiation.

We have characterized the vaccinia virus 11-kd late promoter through 5' and 3' deletions and site-directed mutagenesis. The promoter function appears to be contained within an approximately 30-bp fragment, which after translocation is able to direct RNA synthesis late in infection at a reduced level. We demonstrate that a TAAAT sequence in the proximal part of the promoter is essential for its function. This cis-acting element is highly conserved within vaccinia virus late promoters and overlaps the site of transcription initiation. Deletions or mutations within this conserved element completely inactivate the promoter. The evidence indicates that the TAAAT motif functions as a TATA box. The region immediately upstream of the TAAAT motif determines the promoter strength.