Myb-interacting protein, ATBF1, represses transcriptional activity of Myb oncoprotein

Using the yeast two-hybrid system, the transcription factor ATBF1 was ident ified as v-Myb- and c-Myb-binding protein. Deletion mutagenesis revealed am ino acids 2484-2520 in human ATBF1 and 279-300 in v-Myb as regions required for in vitro binding of both proteins. Further experiments identified leuc ines Leu(325) and Leu(332) of the Myb leucine zipper motif as additional am ino acid residues important for efficient ATBF1-Myb interaction in vitro, I n co-transfection experiments, the full-length ATBF1 was found to form in v ivo complexes with v-Myb and inhibit v-Myb transcriptional activity. Both A TBF1 2484-2520 and Myb 279-300 regions were required for the inhibitory eff ect. Finally, the chicken ATBF1 was identified, showing high degree of amin o acid sequence homology with human and murine proteins. Our data reveal My b proteins as the first ATBF1 partners detected so far and identify amino a cids 279-300 in v-Myb as a novel protein-protein interaction interface thro ugh which Myb transcriptional activity can he regulated.