Removal of histone H1 from intact nuclei alters the digestion of nucleosome core DNA by staphylococcal nuclease.

We have examined the gel profiles of staphylococcal nuclease digests of intact nuclei following different extents of removal of histone H1 by low pH. It was found that the submonomer fragment pattern (i.e. fragments less than 140 base pairs (bp) changed dramatically following removal of H1. The most striking feature of this change was a marked increase in the relative intensity of a band migrating at 102 +/- 4 bp when about 20-50% of the nuclear DNA is rendered acid soluble. All other submonomer bands decreased in relative intensity. There was no evidence for an approximately 100-bp repeat pattern accompanying the enhanced generation of the 102-bp fragment following H1 removal. This result, along with the comparisons of gel profiles for different extents of digestion, suggests that removal of histone H1 from nuclei results in an increased susceptibility of the DNA to staphylococcal nuclease at one or both ends of many of the core particles and that a strong block to further digestion occurs within these core particles resulting in the formation of a relatively stable 102-bp fragment.