Corepressor

As a corepressor ( corepressor ) is called in molecular biology, a substance that inhibits the expression of genes. A corepressor decreases the expression of genes by direct interaction with the operator ( a DNA sequence adjacent to the regulated gene), but indirectly through interaction with proteins that in turn bind to the operator gene.

In protein synthesis by prokaryote it denotes the ligand of a repressor protein as corepressor. For example, the tryptophan repressor ( trpR ) E. coli only able to bind to DNA and to prevent the transcription of the trp operon, when it is bound to its co-repressor tryptophan. Since the Tryptophanrepressor is inactive in the absence of tryptophan, then called it is called aporepressor. Since the trp operon encoding enzymes involved in the tryptophan synthesis, this system provides a negative feedback mechanism dar. This is known as end-product repression.

In eukaryotes, a co-repressor is a protein that binds to transcription factors. Co-repressors downregulate the transcription initiation region of a gene by recruiting histone deacetylase. This catalyzes the cleavage of acetyl groups from lysine residues of histones. Thus, the positive charge is increased in the histones, the electrostatic attraction between the negatively charged DNA and histones, is strengthened, and thus the transcription of DNA is less accessible.