High Mobility Group (HMG) Transcription Factors
HMG transcription factors function globally to establish active or inactive chromatin regions. Additionally, they specifically regulate a limited number of genes. High mobility group (HMG) transcription factors fall into one of three subfamilies. The HMGA subfamily shares AT-hook motifs, which are 9 amino acid segments that bind AT-rich DNA stretches in the DNA minor groove. The HMGB subfamily all contain an HMG Box, which is an 80 amino acid DNA-binding domain consisting of three alpha helices that fold into wedge shape and bind the minor groove of DNA with limited or no sequence specificity. Lastly, the HMGN subfamily binds chromatin inside nucleosomes between DNA spires and the histone octamer. HMGA subfamily members are abundant during embryogenesis but are expressed at low levels in most adult cells. Sox transcription factors, members of the HMGB subfamily, are one of earliest classes of genes expressed during embryonic development and regulate progenitor cell specification and the terminal differentiation of multiple cell types in a wide variety of lineages.