Basic Helix-Loop-Helix (bHLH) Transcription Factors

The transcription factors in this group all share a basic helix-loop-helix (bHLH) protein structure. Members of this family have two highly conserved domains that together make up 60 amino acid residues. The amino-terminal end of the bHLH structure contains the basic domain and binds hexanucleotide DNA sequences called E-boxes; different bHLH subfamilies bind different E-box consensus sequences. The carboxy-terminal end of the bHLH contains the HLH domain, which is responsible for binding to other protein subunits to form homodimeric and heterodimeric complexes. bHLH transcription factors are involved in the regulation of the cell cycle and many developmental processes including cardiovascular development, hematopoiesis, stem cell maintenance, skeletal muscle development, neurogenesis, and embryogenesis. Finally, some bHLH transcription factors induce tumorigenesis-related epithelial-mesenchymal transition (EMT).