Figure 3. Epigenetic modifications and transcriptional activity. Genes that are transcriptionally inactive are assembled in a compact chromatin structure with methylated DNA, deacetylated histones, and histone H3 methylated in lysine 9 and 79 residues. In contrast, transcriptional activation is characterized by an open chromatin structure composed of undermethylated DNA, histone H3 acetylated on lysine 9 and 14 residues, histone H3 methylated on lysine 4 residues, and histone H4 acetylated on lysine 5 and 12 residues.