Epigenetic marks

(tags) Features not directly governed by the genetic code, which include methylation of DNA and covalent modification of histone proteins. The latter may also be tagged with methyl, acetyl, ubiquitin, phosphate, poly(ADP)ribose and other biochemical groups. These groups and their particular pattern of protein modification (e.g. mono-, bi-, tri-methylated at different amino acids and combinations of amino acids) modify the function of the tagged proteins and influence the way genes are expressed.