Substrate specificity of histone acetyltransferases (HATs) in vitro. Review of the in vitro substrate specificity described in mammalian systems for the studied five HAT enzymes, either as a free protein or within their respective macromolecular complexes. Dark grey boxes represent lysine residues highly acetylated, light grey boxes represent residues where weak acetylation activity has been observed, and white boxes represent residues where no acetylation is detected. ND represents residues that have not been tested for acetylation. References [15, 18, 27–34] cited in figure.