Induction of DNA Damage in γ-irradiated Nuclei Stripped of Nuclear Protein Classes: Differential Modulation of Double-strand Break and DNA—protein Crosslink Formation

The influence of chromatin proteins on the induction of DNA double-strand breaks (dsb) and DNA—protein crosslinks (dpc) by γ-radiation was investigated. Low molecular weight non-histone proteins and classes of histones were extracted with increasing concentrations of NaCl, whereas nuclear matrix proteins were not extractable even by 2.0 M NaCl. The yield of dsb increased with progressive removal of proteins from chromatin. Whilst removal of low molecular weight non-histone proteins and histone H1 resulted in small increases in the production of dsb, removal of histones H2A/H2B, all histones, or all proteins led to 18·4, 46·4 and 55·5-fold increases in the yield of dsb, respectively, relative to irradiated cells. Therefore, both histones and non-histone proteins contribute to the radioprotection of DNA, core histones being the major radioprotectors. In contrast, depletion of chromatin proteins caused little or no effect on the induction of dpc until the chromatin was extracted with ≥ 1·4 m NaCl. However, o...