Information contained in the DNA (genes) directs the sequence of amino acids in a protein through messenger RNA (mRNA). The synthesis of mRNA from the DNA template is called transcription, and the synthesis of proteins using the information coded in mRNA is called translation. After the proteins are synthesized they not only acquire a three-dimensional structure but also acquire covalent modification of some of their amino acids. Examples of such modifications are acetylation, phosphorylation, methylation, hydroxylation, and glycosylation. In case of histones present in chromatin, acetylation and methylation are most frequent on lysine and arginine residues and phosphorylation on serine and threonine residues.