DROSOPHILA HOMOLOGS OF THE PROTOONCOGENE PRODUCT PEBP2 CBF-BETA REGULATE THE DNA-BINDING PROPERTIES OF RUNT/

The Drosophila runt gene is the founding member of the Bunt domain fam ily of transcriptional regulators, Mammalian Runt domain genes encode the a subunit of the heteromeric DNA-binding factor PEBP2/CBF. The unr elated PEBP2/CBF beta protein interacts,vith the Runt domain to increa se its affinity for DNA. The conserved ability of the Drosophila Bunt protein to respond to the stimulating effect of mammalian PEBP2/CBF be ta indicated that flies were likely to have a homologous beta protein. Using the yeast two-hybrid system to isolate cDNAs for Runt-interacti ng proteins, we identified two Drosophila genes, referred to as Brothe r and Big-brother, that have substantial sequence homology with PEBP2/ CBF beta. Yeast two-hybrid experiments as well as in vitro DNA-binding studies confirmed the functional homology of the Brother, Big-brother , and PEBP2/CBF beta proteins and demonstrated that the conserved regi ons of the Runt and Brother proteins are required for their heterodime ric interaction, The DNA-bending properties of Bunt domain proteins in the presence and absence of their partners were also examined, Our re sults show that Bunt domain proteins bend DNA and that this bending is influenced by Brother protein family members, supporting the idea tha t heterodimerization is associated with a conformational change in the Bunt domain. Analysis of expression patterns in Drosophila embryos re vealed that Brother and Big-brother are likely to interact with runt i n vivo and further suggested that the activity of these proteins is no t restricted to their interaction with Bunt.