Fig. 1

DNA methylation, histone modifications and chromatin remodeling as regulatory mechanisms of epigenetic gene regulation. DNA methylation represents a process by which methyl groups are transferred onto the 5′ position of a cytosine molecule, commonly in the context of CpG sites, without altering the DNA sequence. Histone modifications include post-translational modifications at the histone N-terminal tails, such as acetylation, methylation and phosphorylation, causing chromatin structure alterations. Changes in nucleosome position are also responsible for rearrangement of chromatin structure, a process known as chromatin remodeling. Nucleosomes can be affected in several ways, including nucleosome sliding, nucleosome ejection and histone eviction. Histone variants add further complexity to epigenetic regulation of the genome. Various histone variants are characterized for H2A, H2B and H3. All these mechanisms are highly interrelated and play an important role in the regulation of gene accessibility to the transcriptional machinery