Histone. Nucleosome structure. Histone proteins bind DNA forming nucleosomes. Two copies of H2A, H2B, H3 and H4 histones form the nucleosome core particle. Epigenetic regulation refers to the post-translational modification of histone tails. In this thesis, the acetylation of histone H3 lysine 27 (H3K27) is used as an epigenetic marker for transcriptionally active euchromatin. The trimethylation of histone H3 lysine 9 (H3K9me3) is used as a marker for transcriptionally repressed or silenced heterochromatin. Not altered. CC. Import and Impact: Characterization of parvovirus-nucleus interactions Elina H. Mäntylä