Methylation been discovered on a spread of lysine residues in numerous 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 domain of histone H4 2 and K26 of histone H1B 3 A number of proteins liable for the methylation of specific residues have been characterized, and all but one in all these accommodates a SET domain