Members of the large SOX family of transcription factors are widely conserved and at least 20 are found in mammals. Structurally SOX proteins exhibit a high mobility group (HMG) motif that binds the DNA minor groove. SOX family members are often found in multiprotein complexes that regulate their ability to affect transcription. SOX proteins play important roles in early development and are often used as markers to assess the differentiation of specific cell lineages.
SOX18 (SRY-related HMG box) is a 41 kDa (predicted) Group F member of the SOX family of DNA-binding proteins. Human SOX18 is 384 amino acids (aa) in length and contains an N-terminal DNA-binding HMG box (aa 85 - 153), a central TAD region (aa 168 - 260) and a highly charged sequence that contains a nine aa transactivation motif (aa 323 - 331). SOX18 is expressed by endothelium and vascular smooth muscle, and apparently promotes the formation and organization of new capillaries. Over aa 276 - 384, human SOX18 shares 90% and 89% aa identity with mouse and porcine SOX18, respectively.