The interaction of platinum complexes with nucleosomes investigated with fluorescent probes

The fluorescent probes, N,-(3-pyrene)maleimide, which is specific for histone H3, and terbium (Tb3+), which is specific for guanine single-stranded residues in DNA, are used to investigate the interaction of platinum complexes (cis- and trans-dichlorodiammineplatinum(II)) with rat liver and calf thymus nucleosomes. At low concentrations of the drug, lower than most of those reported previously in studies investigating the interaction of the drugs with isolated DNA, N-(3-pyrene)maleimide studies show that profound modifications occur near or in the cysteinyl binding site of histone H3. H3 dimer formation appears to be the cause of the change induced by trans-DDP; however, the effects observed with the cis-isomer do not seem to be correlated with dimer formation. At short incubation times, Tb3+ fluorescence shows small changes in DNA conformation, but they are slight when compared to the effect observed with proteins at the same length of incubation. SDS-polyacrylamide gels indicate some changes in protein composition, and agarose gels display a decrease in ethidium bromide staining of the cis-treated DNA. The results suggest that the protein portion, predominantly histone H3, as well as DNA are targets for the platinum derivatives in the nucleosome.