ABSTRACT
Epigenetics relies on enzymatic modifications of DNA and histones. The epigenetic modification of DNA in mammals is mainly or entirely enzymatic methylation of some cytosines 50 to guanines. Histone modification is more complex and involves several enzymatic covalent additions of which methylation and acetylation are discussed here. The substrates for these modifications come from metabolism and may, to various degrees, respond to environmental influences such as diet and stressrelated changes in metabolic regulation. Methylation of DNA nearly always results in gene silencing; however, methylation of histones can promote either gene silencing or activation and thus influences on epigenetics through methyl metabolism may be constrained by these competing influences on histone methylation. Histone acetylation nearly always results in gene activation and thus the effects of acetyl metabolism on epigenetics are potentially stronger because they act in one direction.
