[2] One class of transcription coregulators modifies chromatin structure through covalent modification of histones.
Histones are rich in lysine residues which at physiological pH are protonated and therefore positively charged.
The electrostatic attraction between these opposite charges is largely responsible for the tight binding of DNA to histones.
These HAT proteins are able to acetylate the amine group in the sidechain of histone lysine residues which makes lysine much less basic, not protonated at physiological pH, and therefore neutralizes the positive charges in the histone proteins.
A common feature of nuclear receptor coactivators is that they contain one or more LXXLL binding motifs (a contiguous sequence of 5 amino acids where L = leucine and X = any amino acid) referred to as NR (nuclear receptor) boxes.