Corepressor

A corepressor is a molecule that binds to a sequence-specific DNA binding protein and enables that protein to direct transcriptional repression. The term is used to apply to two types of mechanism. In the first case, a small molecule binds to and effects a conformational change in a DNA-binding protein, thus, enabling binding to a specific DNA sequence. One example of this mode of action is the binding of tryptophan to the tryptophan repressor. The second type of corepressor is a protein that forms a specific complex with a sequence-specific DNA binding protein and then itself inhibits transcription either directly or indirectly. One example of such an activity is the complex formed in eukaryotes between histone deacetylases and DNA-targeted regulators via an adaptor protein.