Binding of hedamycin to deoxyribonucleic acid and chromatin of testis and liver

The binding of the antibiotic hedamycin to DNA was evaluated by density gradient centrifugation in CsCl to determine the type I binding, which is essentially irreversible at high and low ionic strength. Exhaustive dialysis at low ionic strength was used to determine the sum of type I and type II binding (irreversible at low ionic strength but reversible at high ionic strength). The maximum ratio of hedamycin to DNA nucleotides (rf) is 0.1 for type I and 0.1 for type II binding to free DNA, but these ratios decrease to 0.07--0.08 in chromatin of rat liver and a testis fraction (spermatogonia plus primary spermatocytes). The rf for type I binding of hedamycin to monomeric nucleosomes of this testis fraction is considerably less than maximum binding to polymeric nucleosomes or chromatin, suggesting that hedamycin binds more effectively to "linker" DNA than to DNA attached to the core of the nucleosomes. Hedamycin binding to the chromatin of the spermatid fraction of testis is greatly decreased in comparison with chromatin of early stages; this correlates with the change from nucleohistones to nucleoprotamines at the middle to late spermatid stages of spermiogenesis.