Figure 1.

Levels of epigenetic regulation. The DNA sequence can be methylated at cytosine residues in a CpG context, termed DNA methylation. DNA is wrapped around the histone octamer to form the nucleosome. Variants and post-translational modifications of these histone proteins form another layer of epigenetic regulation. The state of these epigenetic modifications together determines whether the chromatin will be organised in an accessible ‘open’ or an inaccessible ‘closed’ state. Higher order folds and loops organise the chromatin into active and inactive compartments.