Inhibitor of DNA binding protein

Inhibitor of DNA binding/differentiation proteins, also known as an "Id proteins," actually comprise a family of proteins that heterodimerize with basic helix-loop-helix (bHLH) transcription factors to inhibit DNA binding of bHLH proteins. Id proteins lack DNA binding domains and thus negatively regulate bHLH transcription factors when they bind the bHLH active site. Some vertebrates are known to have any of four types of Id proteins (called Id1, Id2, Id3, and Id4). They all belong to the basic helix-loop-helix family of transcription factors. Perk et al. reported in a review paper that there is "circumstantial evidence for the importance of the Id proteins in tumour cell biology." These proteins could thus be important in human efforts to understand cancer.