Along with ubiquitination and phosphorylation, methylation is a major biochemical process for modifying protein function.  The most prevalent protein methylations affect arginine and lysine residue of specific histones. Otherwise histidine, glutamate, asparagine, cysteine are susceptible to methylation.  Some of these products include S-methylcysteine, two isomers of N-methylhistidine, and two isomers of N-methylarginine.