abstract:Inhibitor of DNA-binding/differentiation proteins, also known as Id proteins comprise a family of proteins that heterodimerize with basic helix-loop-helix (bHLH) transcription factors to inhibit DNA binding of bHLH proteins. Id proteins also contain the HLH-dimerization domain but lack the basic DNA-binding domain and thus negatively regulate bHLH transcription factors when they heterodimermize with bHLH proteins.