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.
SOX15 (also known as SOX20) is a nuclear, 25 kDa transcriptional repressor that belongs to group G of the SOX gene family. Human SOX15 is 233 amino acids (aa) in length and contains a 63 aa DNA-binding HMG-box (amino acids 48 - 110). Although the C-terminus (aa 126 - 233) does not bind DNA, it is required for SOX15 repressive activity. It may accomplish this by interacting with β-catenin. SOX15 is expressed in myoblasts and regulates skeletal muscle regeneration and differentiation. Human SOX15 shares 75% aa sequence identity with mouse SOX15.