ID2: ProductsID2 (Inhibitor of DNA binding 2; also known as inhibitor of differentiation 2) is a 15 kDa member of the small ID HLH family of proteins. It is a nuclear protein that forms inactivating heterodimers with bHLH transcription factors. bHLH proteins activate lineage-specific genes and ID2. Human ID2 is 134 amino acids (aa) in length. It contains one HLH domain (aa 36 - 76) but no DNA-binding motif. Full-length human ID2 is 98% aa identical to both mouse and porcine ID2.