Histone methyltransferases (HMT) are enzymes which catalyze the transfer of one to three methyl groups from the cofactor s-adenosylmethionine to lysine and arginine residues of histone proteins. These proteins have been characterized by a SET (Su(var)3-9, Enhancer of Zeste, Trithorax) domain, however the recently discovered HMT Dot1 lacks the characteristic SET domain.
