Transcription factor that binds to DNA at the consensus sequence 5'-AACAAT-3' (PubMed:10871192). Binds to the proximal promoter region of the myelin protein MPZ gene, and may thereby be involved in the differentiation of oligodendroglia in the developing spinal tube (By similarity). Binds to the gene promoter of MBP and acts as a transcriptional repressor (By similarity). Binds to and modifies the activity of TCF7/TCF1, thereby inhibiting transcription and modulates normal gamma-delta T-cell development and differentiation of IL17A expressing gamma-delta T-cells (By similarity). Regulates expression of BLK in the differentiation of IL17A expressing gamma-delta T-cells (By similarity). Promotes brown adipocyte differentiation (By similarity). Inhibitor of WNT signaling (PubMed:20028982). Homodimer; homodimerization reduces DNA binding efficiency (PubMed:10871192). Interacts with TCF7/TCF1 long isoform (via N-terminus); inhibits WNT-mediated transcriptional activity (PubMed:17218525, PubMed:20028982). Interacts with HHEX (via N-terminus); abolishes the SOX13-mediated inhibition of WNT-mediated transcriptional activity via competitive inhibition of the SOX13-TCF7 complex (PubMed:20028982). Expressed in exocrine cells and islets of Langerhans in the pancreas (at protein level) (PubMed:10871192). Expressed in the pancreas, placenta, kidney, brain, heart, lung, and liver (PubMed:10871192, PubMed:20028982). Expressed in adipose tissue, cervix, colon, esophagus, ovary, prostate, small intestine, spleen, testicle, thymus and thyroid (PubMed:20028982). Autoantibodies against SOX13 are present in sera from patients with type 1 diabetes. Several frameshifts.