The Role of the Central Globular Domain of Histone H5 in Chromatin Structure

Abstract Histone H5 contains three tryosines in the central, a polar region of the molecule. All three tryosines can be spin labeled at low ionic strength. When the central globular domain is folded at high ionic strength, only one tyrosine becomes accessible to the imidazole spin label. Spin labeling the buried tyrosines prevents the folding of the globular structure, which, in turn, affects the proper binding of the H5 molecule to stripped chromatin. Chromatin complexes reconstituted from such an extensively modified H5 molecule show a weaker protection of the 168 base pair chromatosome during nuclease digestion. However, when only the surface tyrosine of the H5 molecule is labeled, such a molecule can still bind correctly to stripped chromatin, yielding a complex very similar to that of native chromatin. Our data supports the idea that not just the presence of the linker histone H5, but the presence of an intact H5 molecule with a folded, globular central domain is essential in the recognition of its s...