Functional Characterization of Multiple Transactivating Elements in β-Catenin, Some of Which Interact with the TATA-binding Proteinin Vitro *

β-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 β-catenin undergoes nuclear translocation and serves as transcriptional coactivator of T cell factor DNA-binding proteins. Previously the transactivation potential of different portions of β-catenin has been demonstrated, but the precise location of transactivating elements has not been established. Also, the mechanism of transactivation by β-catenin and the molecular basis for functional differences between β-catenin and the closely related proteins Armadillo and Plakoglobin are poorly understood. Here we have used a yeast system for the detailed characterization of the transactivation properties of β-catenin. We show that its transactivation domains possess a modular structure, consist of multiple subelements that cover broad regions at its N and C termini, and extend considerably into the Armadillo repeat region. Compared with β-catenin the N termini of Plakoglobin and Armadillo have different transactivation capacities that may explain their distinct signaling properties. Furthermore, transactivating elements of β-catenin interact specifically and directly with the TATA-binding proteinin vitro providing further evidence that a major function of β-catenin during Wnt signaling is to recruit the basal transcription machinery to promoter regions of Wnt target genes.