cis-Diamminedichloroplatinum (II) modified chromatin and nucleosomal core particle probed with DNase I

Chromatin and nucleosomal core particles were modified with cis-diamminedichloroplatinum (II) and the nucleoprotein complexes then digested with DNase I. Limited digestion of the modified chromatin containing cis-Pt(NH3)2Cl2 mediated cross-links involving the non-histone chromosomal proteins (Scovell et al. (1987) Biochem. Biophys. Res. Commun. 142, 826-835) does not release the low mobility proteins and excises only about 20% of the high mobility proteins 1, 2, and E. This supports previous findings that the low mobility proteins are involved primarily in protein-protein cross-links. In addition, the covalent cross-links between DNA and the high mobility proteins 1, 2, and E are relatively inaccessible to DNase I, in marked contrast to their accessibility to micrococcal nuclease. Furthermore, gels of the denatured DNA fragments obtained from digestion of both modified chromatin and nucleosomal core particle reveal virtually no difference in the 10n base repeat pattern, indicating no detectable change in the DNA-protein interactions upon DNA modification. This suggests that the predominant modification produced on core particle DNA, whether contained within higher order chromatin structure or in the core particle itself, is one which does not significantly alter the helical twist of the DNA within these nucleoprotein assemblies.