Epigenetics in Health and Disease

4. DNA methylation as epigenetic mechanism

DNA methylation is a covalent modification of nucleotides, in which a methyl group is added to a cytosine residue at position C-5 or N-4 or to an adenine residue at position N-6. In terms of evolution, it is one of the most ancient epigenetic mechanisms for the regulation of gene expression and the timing and sequence specific targeting of its addition or removal from DNA affects the timing and targeting of events of cellular regulation. DNA methylation is found in almost all life forms, including bacteria, plants, and mammals, but it is lost in organisms such as S. cerevisiae, S. pombe, C. elegans, and Drosophila. However, several reports suggest that DNA methylation does occur in the fruit fly; whether ...