Histone-histone interactions. II. Structural stability of the histone H3-H4 complex

The stability of the histone H3-H4 complex toward urea, changes in pH and ionic strength, and certain chemical modifications have been examined by gel electrophoresis anc circular dichronism. When uncomplexed, the two cysteine residues of histone H3 become rapidly oxidized, forming an intramolecular disulfide bridge which apparently blocks complex formation on return to complexing conditions. The complex was found to be unstable toward low values of pH and ionic strength, concentrations of urea exceeding 1 M, modifications of the cysteine residues, and fragmention in which the C terminal portions of either H3 or H4 are removed. A possible structure for this complex is proposed.