Histone methyltransferase

Histone methyltransferases (HMT) are enzymes, histone-lysine N-methyltransferase and histone-arginine N-methyltransferase, that catalyze the transfer of one to three methyl groups from the cofactor S-Adenosyl methionine to lysine and arginine residues of histone proteins. These proteins often contain a SET (Su(var)3-9, Enhancer of Zeste, Trithorax) domain, however the recently discovered HMT Dot1 lacks the characteristic SET domain.

Role in gene regulation
Histone methylation serves in epigenetic gene regulation. Methylated histones bind DNA more tightly, which inhibits transcription.

Methylated histones can either repress or activate transcription as different experimental findings suggest. See Histone.