A sedimentation study of the interaction of superhelical SV40 DNA with H1 histone

By moving boundary sedimentation it is shown that the interaction of H1 histone with superhelical circular SV40 DNA results in the formation of giant heterogeneous aggregates. The size of these aggregates grows with increasing H1 concentration. s20,w values of some 10 000 S were measured. As compared with open relaxed circular DNA a preferential interaction of superhelical DNA with H1 histone is observed, irrespective of the sign of the superhelical turns which was reversed by the addition to DNA of ethidium bromide. The addition to the H1 complexed aggregates of ethidium bromide effects a progressive breakdown of the aggregates. Furthermore, the superhelicity of DNA is not changed by the addition of small amounts of H1 histone.