Acetylation of Conserved Lysines

The N-terminal histone tails of the four core histone proteins contain several residues of the aminoacid lysine. The aminoacid sequence of these histone tails and especially the position of these lysines are strongly conserved in all eukaryotic cells, i.e. all cells that contain a cell nucleus. This includes yeast cells and human cells. The amino acid lysine has a positively charged amino group in its side chain located at the epsilon-carbon and hence called the epsilon-amino group. This amino group can be acetylated by an enzyme in the cell, histone acetyletransferase (HAT). This reaction can be reversed by an enzymatic activity in the cell called histone deacetylase (HDA). The presence of a positive charge on the lysine amino acids of the histone tails should increase the potential for electrostatic interactions with the negatively charged phosphate backbone of DNA and for negatively charged patches on the histone octamers

Active genes are usually located in hyperacetylated chromatin while inactive genes are found in hypoacetylated chromatin. Furthermore, transcription factors which stimulate transcription from various genes have been shown to recruit HAT activity to the promoters of these genes while other factors which are known to inhibit or repress transcription have been shown to recruit HDA activity to these promoters which results in hypoacetylation of surrounding histones. In this context it is important to note that active genes have a more open structure while inactive genes are more condensed and tightly packed. The functional and structural basis for these effects are not clear but a hypothetical picture of what may be happening is presented here:

A hypothesis on the effect on chromatin by acetylation of histone tails »