INHIBITION OF THE DNA-BINDING ACTIVITY OF DROSOPHILA SUPPRESSOR OF HAIRLESS AND OF ITS HUMAN HOMOLOG, KBF2 RBP-J-KAPPA, BY DIRECT PROTEIN-PROTEIN INTERACTION WITH DROSOPHILA HAIRLESS/

We have purified the sequence-specific DNA-binding protein KBF2 and cl oned the corresponding cDNA, which is derived from the previously desc ribed RBP-J kappa gene, the human homolog of the Drosophila Suppressor of Hairless [Su(H)] gene. Deletion studies of the RBP-J kappa and Su( H) proteins allowed us to define a DNA binding domain conserved during evolution. Because Su(H) mutant alleles exhibit dose-sensitive intera ctions with Hairless (H) loss-of-function mutations, we have investiga ted whether the RBP-J kappa or Su(H) proteins directly interact with t he H protein in vitro. We show here that H can inhibit the DNA binding of both Su(H) and RBP-J kappa through direct protein-protein interact ions. Consistent with this in vitro inhibitory effect, transcriptional activation driven by Su(H) in transfected Drosophila S2 cells is inhi bited by H. These results support a model in which H acts, at least in part, as a negative regulator of Su(H) activity. This model offers a molecular view to the antagonistic activities encoded by the H and Su( H) genes for the control of sensory organ cell fates in Drosophila. We further propose that a similar mechanism might occur in mammals.