DBP, HLF and TEF comprise a distinct subfamily of mammalian bZIP proteins that 
plays an important role in regulation of tissue-specific gene expression, 
particularly in the liver. In this report we demonstrate that DBP contains a 38 
amino acid TAD which is highly homologous to the HLF and TEF TADs that we have 
delineated previously. Deletion of this domain completely abrogates 
transcriptional activity of native DBP and GAL4-DBP fusion proteins. This domain 
functions as a modular TAD that is a potent transcriptional activator when fused 
to the GAL4 DBD. While DBP itself is a liver-specific transactivator, the DBP 
TAD is active in a variety of cell types, indicating that liver-specific 
activity is not an intrinsic property of the TAD and must be conferred by other 
regions of the protein. Using GAL4-HLF fusion proteins, we further refine the 
core TAD of PAR proteins to a region of 13 amino acids. Recently described 
PAR-bZIP proteins from Drosophila and zebrafish also contain domains that share 
strong homology with the TAD of mammalian PAR proteins, making this one of the 
most highly evolutionarily conserved TADs identified to date.