DIFFERENT CORE PROMOTERS POSSESS DISTINCT REGULATORY ACTIVITIES IN THE DROSOPHILA EMBRYO

There are numerous examples of shared enhancers interacting with just a subset of target promoters. In some cases, specific enhancer-promote r interactions depend on promoter competition, whereby the activation of a preferred target promoter precludes expression of linked genes. H ere, we employ a transgenic embryo assay to obtain evidence that promo ter selection is influenced by the TATA element. Both the AE1 enhancer from the Drosophila Antennapedia gene complex (ANT-C) and the IAB5 en hancer from the Bithorax complex (BX-C) preferentially activate TATA-c ontaining promoters when challenged with linked TATA-less promoters. I n contrast, the rho neuroectoderm enhancer (NEE) does not discriminate between these two classes of promoters. Thus, certain upstream activa tors, such as Ftz, prefer TATA-containing promoters, whereas other act ivators, including Dorsal, work equally well on both classes of promot ers. These results provide in vivo evidence that different core promot ers possess distinct regulatory activities. We discuss the possibility that an invariant TFIID complex can adopt different conformations on the core promoter.