Fig. 1

Comparison of Internal vs N-terminal histone modifications. a Internal (In) modifications are deposited on the side chain of internal amino acids on the octameric core domain or the N-terminal tails of histone proteins. Conversely, N-alpha terminal (Nt) marks are located at the N-terminal end of histone tails. b A HAT catalyzes the transfer of an acetyl group from Ac-CoA to the ε-amino group of an internal lysine residue. N^ε-lysine acetylation is reversed by HDACs. c NATs transfer an acetyl group from Ac-CoA to the α-amino group of the first amino acid residue at the N-terminal tip of histone proteins. N-alpha terminal acetylation is believed to be static as no NDACs have been identified yet. d A variety of In-me are currently known to occur on different residues including lysine, arginine, and glutamine. As an example the mono-, di- or trimethylation of internal lysine ε-amino groups is catalyzed by KMTs using SAM as the methyl donor. The lysine demethylase reaction is driven by KDMs (LSD1 and JmjC domain-containing proteins). e The mono-, di- and trimethylation of the α-amino group on the first amino acid residue of histones is catalyzed by NTMTs using SAM as the methyl donor. N-alpha terminal methylation is described as a constitutive PTM as NTDMs remain to be discovered