Transcription activator. Binds to the DNA sequence 5'-AACAAT-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 (including endodermin and dhh/chh) and indirectly. Also represses wnt-responsive genes to inhibit wnt/beta-catenin signaling (By similarity). Interacts (via C-terminus) with ctnnb1/beta-catenin (via Armadillo repeats); this interaction is required for inhibition of wnt-signaling. Expressed throughout the deep and superficial endoderm during gastrulation. During neural and early tail bud stages, expression declines significantly in the anterior endoderm, except in the endoderm behind the cement gland. Strong expression persists in the endoderm posterior to the liver diverticulum until late tail bud stage. By late tailbud, expression is undetectable in most of the endoderm but is maintained in the presumptive gall bladder region and the extreme posterior region. In addition, expressed in endothelial cells in the head and along the flank of the embryo. The 9aaTAD motif is a transactivation domain present in a large number of yeast and animal transcription factors.