NCIt definition : bHLH class proteins are sequence-specific DNA-binding proteins that contain a conserved
50-amino acid HLH domain consisting of two alpha-helices separated by a variable loop
sequence, adjacent to a sequence that is highly enriched in basic amino acids. The
HLH region mediates protein dimerization, while the basic region mediates sequence-specific
DNA binding. Many bHLH proteins recognize a DNA sequence known as the E box. Class
A bHLH proteins are ubiquitously expressed, while class B bHLH proteins are expressed
in specific cell types. In general, class B proteins preferentially bind to DNA as
heterodimers with class A proteins and function as transcriptional activators.;