Histone H3 disulfide dimers and nucleosome structure.

The arginine-rich histone, H3, isolated from avian erythrocytes, can dimerize by forming a disulfide linkage between the single cysteine sulfhydryl residues at position 110 of the H3 polypeptide chain. The H3 dimer can be substituted for undimerized H3 in experiments in which the nucleosome is reconstituted from DNA and mixtures of the four "core" histones, H2A, H2B, H3, and H4. We report here that reconstituted nucleosomes containing H3 dimer are indistinguishable, by a number of criteria, either from native nucleosomes or from reconstitutes containing H3 monomer. The criteria include the pattern of susceptibility of the complex to nucleases, the amount of DNA supercoiling induced by histone binding, and the hydrodynamic properties of reconstituted nucleosome "core" preparations. The results suggest that the residues in the neighborhood of position 110 on each H3 molecule are in close contact in the nucleosome. If, as has been proposed, the nucleosome has a dyad axis, then the disulfide bridge between H3 molecules must lie on this axis.