Selective radiolabelling and identification of a strong nucleosome binding site on the globular domain of histone H5

We describe a chemical investigation of the nucleosome binding site(s) on histone H5. Selective radiolabelling by reductive methylation has led to the identification of lysine residues in H5 that are protected by its association with chromatin. The most strongly protected lysine is Lys-85 which occurs in the globular domain, in a region that is highly conserved between H5 and H1, and in H1 variants, and which probably constitutes a strong binding site for DNA where it enters and leaves the nucleosome. Lysines in the amino-terminal and lysine-rich carboxy-terminal tails are only weakly protected against chemical modification, suggesting a different mode of interaction with DNA.