Studies on histone H1 condensing properties in complexes with DNA and polydeoxyribonucleotides using netropsin as a probe.

The binding of histone H1 with DNA and synthetic DNA duplex polymers with respect to its property to induce higher ordered structures has been studied using the DNA binding antibiotic netropsin as a probe. It was shown that the formation of distinct steps of different condensed structures (double-fibers, cable- and stem-like forms) is influenced by the ionic strength. CD titration data of DNA-H1 complexes with netropsin at 20 mM NaCl indicated no change in the binding to strong affinity sites (dA X dT clusters) as compared to free DNA's, while weak netropsin binding regions are strongly affected by competition interaction with H1. At low histone concentration the presence of netropsin favours the formation of double fibers. CD and electron microscopic findings indicated that at 20 mM NaCl the occurrence of condensed structures of DNA histone H1 complexes is not dependent on the base content. The major groove interaction of H1 most probably plays the major role in the formation of higher ordered structures. However, the minor groove binding might be involved as a secondary event. A hierarchy of relevant morphological structures observed for DNA-H1 complexes is presented.