question: Which histone modifications are associated with constitutive heterochromatin?
answer: Strong methylation at H3 lysine 9 occurred preferentially in heterochromatic chromocenters of Arabidopsis nuclei. In general, heterochromatin has been linked to trimethylation of H3 at lysine 9 and parsimony analysis reveal that histone H3K9 methylation is, next to histone deacetylation, the evolutionary most stable heterochromatic mark. Classical histone modifications associated with heterochromatin also include H3K27me1 and H3K27me2. H3K36me3 function is not restricted to actively transcribed regions only and may contribute to the composition of heterochromatin. Other histone methylation marks usually found in constitutive heterochromatin are H4K20me3, H3K9me3, and H3K79me3. H3S10P is a good marker of pericentromeric heterochromatin.