The effect of H3K79 dimethylation and H4K20 trimethylation on nucleosome and chromatin structure

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Abstract
Histone methylation has important consequences for chromatin activity. Now, histones with methyllysine analogs are used to reconstitute nucleosomes: the crystal structures show no global changes in nucleosomes with H3K79me2 and H4K20me3, but the latter modification enhances compaction of nucleosomal arrays. Histone methylation regulates chromatin function dependent on the site and degree of the modification. In addition to creating binding sites for proteins, methylated lysine residues are likely to influence chromatin structure directly. Here we present crystal structures of nucleosomes reconstituted with methylated histones and investigate the folding behavior of resulting arrays. We demonstrate that dimethylation of histone H3 at lysine residue 79 locally alters the nucleosomal surface, whereas trimethylation of H4 at lysine residue 20 affects higher-order structure.