why does histone methylation occur over large areas of chromatin
Histone methylation The genome is tightly condensed into chromatin, which needs to be loosened for transcription to occur. In order to halt the transcription of a gene the DNA must be wound tighter. This can be done by modifying histones at certain sites by methylation. Histone methyltransferases are enzymes which transfer methyl groups from S-Adenosyl methionine onto the lysine or arginine residues of the H3 and H4 histones. There are instances of the core globular domains of histones being methylated as well.