By doing this, the DNA is more accessible and leads to more transcription factors being able to reach the DNA. Thus, acetylation of histones is known to increase the expression of genes through transcription activation. Deacetylation performed by HDAC molecules has the opposite effect.
Subsequently, one may also ask, why are histone modifications important?
Histone modifications also play an important role in epigenetic regulation. Histones are highly basic proteins that act as spools around which DNA winds in chromatin. This compacting allows the DNA to fit into a much smaller space than it would otherwise.
What does methylation of histone tails do?
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.