Question

What histone modification causes chromatin to relax/decondense? What enzyme adds this modification? What enzyme removes it?

Answer 1

The methylation of histone, mainly in H3 and H4 subunits of histone octamer, causes chromatin relax or condense. The methylation of histone can either increase or decrease transcription of genes, depending on which amino acid is methylated in histone and how many methyl groups are attached to the histone. Single methylation event in 20th lysine residue in the H4 subunit can reduce the attraction between the histone and the DNA, thus looses the DNA for transcription of a gene located on the DNA. Where as the triple (three) methylation at lysine 20 of H4 is responsible for chromatin repression e. i. the DNA binds with the histone octamer more tightly.

The enzyme that add the methyl groups in this modification is histone methyltransferase.

The enzyme that removes the methyl groups from histone is histone demethylase.