ADF-1 IS A NONMODULAR TRANSCRIPTION FACTOR THAT CONTAINS A TAF-BINDING MYB-LIKE MOTIF

Adf-1 is an essential Drosophila melanogaster sequence-specific transa ctivator that binds the promoters of a diverse group of genes. We have performed a comprehensive mapping of the functional domains of Adf-1 to study the role of transactivators in the process of gene activation , Using a series of clustered point mutations and small deletions rye have identified regions of Adf-1 required for DNA binding, dimerizatio n, and activation, In contrast to most enhancer-binding factors, the A df-1 activation regions are nonmodular and depend on an intact protein , including the Adf-1 DNA-binding domain, for activity, Like many tran scriptional activators, Adf-1 contains a TFIID-binding domain that can interact with specific TAF subunits. Although TAFs are required for A df-1-directed activation, TAF binding is not sufficient, suggesting th at Adf-1 may direct multiple essential steps during activation, Intere stingly, both the TAF-binding domain and the DNA-binding domain contai n sequences homologous to those of the Myb family of DNA-binding domai ns, Thus. Adf-1 has evolved an unusual structure containing two versio ns of the Myb motif, one that binds DNA and one that binds proteins.