basic helix-loop-helix

Function

• basic region forms half site for DNA-binding
• most proteins with a helix-loop-helix (HLH) have an extra basic region of about 15 amino acid residues, adjacent to the HLH that specifically binds to DNA
  • bHLH proteins may be
    • class A (ubiquitous)
    • class B (tissue-specific)
• members of the bHLH family bind variations on the core sequence 'CANNTG', also refered to as the E-box motif

Structure

• the homodimerization or heterodimerization mediated by the HLH domain is independent of, but necessary for DNA binding
• that is, two basic regions are required for DNA binding activity
• HLH proteins lacking the basic domain function as negative regulators since they form heterodimers, but fail to bind DNA

More general terms

• basic DNA-binding motif
• helix-loop-helix (HLH)