Methylation been discovered on a variety of lysine residues in various histones: K4 (using the one-letter amino-acid code for lysine), K9, K27, K36 and K79 in histone H3, K20 in histone H4, K59 in the globular area of histone H4 2 and K26 of histone H1B 3 A number of proteins accountable for the methylation of specific residues have been characterised, and all however considered one of these contains a SET domain