Methylation been discovered on a range of lysine residues in varied histones: K4 (using the only-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 Several proteins chargeable for the methylation of specific residues have been characterized, and all however one of these incorporates a SET area