Chromatin structure during bleomycin-induced DNA damage and repair.

We have demonstrated that treatment of human erythroleukemia (K562) cells with bleomycin, an agent known to create both double and single DNA breaks through an oxygen-radical-dependent mechanism, alters higher order chromatin structure (supercoiling) as shown by a reduction in the rate of sedimentation of nucleoids from bleomycin-treated cells. This agent, however, did not appear to induce generalized changes in the organization of chromatin at the nucleosomal level as determined either by rates of digestion of nuclear DNA or by gel electrophoresis of DNA fragments obtained by limited digestion of nuclear DNA. We conclude that while higher chromatin structure is altered by bleomycin damage, organization at the nucleosomal level remains largely conserved.