Functional characterization of multiple transactivating elements in beta-catenin, some of which interact with the TATA-binding protein in vitro

beta-Catenin, a member of the family of Armadillo repeat proteins, plays a dual role in cadherin-mediated cell adhesion and in signaling by Wnt growth factors, Upon Wnt stimulation beta-catenin undergoes nuclear translocation and serves as transcriptional coactivator of T cell factor DNA-binding pro teins. Previously the transactivation potential of different portions of be ta-catenin has been demonstrated, but the precise location of transactivati ng elements has not been established. Also, the mechanism of transactivatio n by beta-catenin and the molecular basis for functional differences betwee n beta-catenin and the closely related proteins Armadillo and Plakoglobin a re poorly understood. Here we have used a yeast system for the detailed cha racterization of the transactivation properties of beta-catenin. We show th at its transactivation domains possess a modular structure, consist of mult iple subelements that cover broad regions at its N and C termini, and exten d considerably into the Armadillo repeat region. Compared with beta-catenin the N termini of Plakoglobin and Armadillo have different transactivation capacities that may explain their distinct signaling properties. Furthermor e, transactivating elements of beta-catenin interact specifically and direc tly with the TATA-binding protein in vitro providing further evidence that a major function of beta-catenin during Wnt signaling is to recruit the bas al transcription machinery to promoter regions of Wnt target genes.