|MoBio||Histone Acetylation, DNA Methylation and Epigenetics||Chapter 4|
Acetylation of the lysine residues at the N terminus of histone proteins removes positive charges, thereby reducing the affinity between histones and DNA. This makes RNA polymerase and transcription factors easier to access the promoter region. Therefore, in most cases, histone acetylation enhances transcription while histone deacetylation represses transcription.
Histone acetylation is catalyzed by histone acetyltransferases (HATs) and histone deacetylation is catalyzed by histone deacetylases (denoted by HDs or HDACs). Several different forms of HATs and HDs have been identified. Among them, CBP/p300 is probably the most important, since it can interact with numerous transcription regulators.
DNA methylation is the addition of a methyl group (CH3) to the DNA's cytosine base. It may affect gene transcription through several different mechanisms (Illustration). The methylation pattern is heritable after cell division (Illustration). Therefore, DNA methylation plays an important role in cell differentiation during development.
Epigenetics is the study of heritable changes in chromatin (e.g., DNA methylation) without involving the change in DNA sequences.