Effect of Histone HI Removal on the Distribution of Ultraviolet-Induced Deoxyribonucleic Acid Repair Synthesis within Chromatin

Because histone H1 plays an important role in the organization of chromatin, we have examined its possible involvement in determining the distribution within chromatin of nucleotides incorporated by UV-induced DNA repair synthesis. It has been shown previously that immediately after repair synthesis almost all of the newly incorporated nucleotides are rapidly digested to acid-soluble form by staphylococcal nuclease [Smerdon, M. J., & Lieberman, M. W. (1980) Biochemistry 19, 2992-3000]. The selective removal of histone H1 from intact nuclei by low pH does not alter this enhanced nuclease sensitivity and, therefore, does not induce any rearrangements of chromatin structure (as detected by staphylococcal nuclease) in newly repaired regions of DNA. However, H1 removal results in 5-12% of the bulk DNA in nuclei becoming more nuclease sensitive. We conclude that, prior to nucleosome rearrangement, either newly repaired regions of DNA lack histone H1 or, if present, this histone confers less resistance to the digestion of these regions by staphylococcal nuclease than to the digestion of the bulk of the DNA in chromatin. Furthermore, following nucleosome rearrangement in newly repaired regions of DNA, removal of histone H1 does not restore the enhanced nuclease sensitivity of these regions. Thus, the increased resistance to nuclease digestion acquired by these regions during nucleosome rearrangement is not conferred in any simple way by the presence of histone H1. Finally, examination of the electrophoretic profiles of the submonomer fragments generated by staphylococcal nuclease from newly repaired DNA and bulk DNA indicates that following nucleosome rearrangement (at least within 30 min) histone H1 is present in most (or all) of the newly repaired regions of DNA.