Transcription activator. Doesn't appear to bind to the consensus 5'-AACAAT-3' DNA binding site, but binds 5'-ATTGTT-3'. All of the sox17 proteins are required for embryonic endoderm development and gastrulation movements, and show some redundancy in function. In addition, the sox17 proteins have distinct but overlapping roles in later gut development. Acts downstream of vegt-signaling in endoderm differentiation to induce a range of endodermal genes both directly and indirectly. Also represses wnt-responsive genes to inhibit wnt/beta-catenin-mediated signaling (By similarity). Interacts (via C-terminus) with ctnnb1/beta-catenin (via Armadillo repeats); this interaction is required for inhibition of wnt-signaling. The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors.