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.
SOX21 is a member of the B group of the SOX family HMG-box transcription factors. It is a 276 amino acid residue protein that has an N-terminal HMG-box and a C-terminal domain that is required for the SOX21 neurogenesis function. Human and mouse SOX21 share 99% amino acid sequence identity.