  The effects of monovalent (Na+, K+) and divalent (Mg2+, Ca2+, Mn2+) ions on
the interaction between DNA and histone are studied using the molecular combing
technique. Lamda-DNA molecules and DNA-histone complexes incubated with metal
cations (Na+, K+, Mg2+, Ca2+, Mn2+) are stretched on hydrophobic surfaces, and
directly observed by fluorescence microscopy. The results indicate that when
these cations are added into the DNA solution, the fluorescence intensities of
the stained DNA are reduced differently. The monovalent cations (Na+, K+)
inhibit binding of histone to DNA. The divalent cations (Mg2+, Ca2+, Mn2+)
enhance significantly the binding of histone to DNA and the binding of the
DNA-histone complex to the hydrophobic surface. Mn2+ also induces condensation
and aggregation of the DNA-histone complex.
