Interaction between lysine-rich histones and DNA

Abstract

Using a membrane filter retention technique we have studied the interaction between DNA and lysine rich histone H5 in vitro. It is found that, depending on the ionic conditions, H5 can bind DNA in a random or cooperative manner and exhibits a preference to DNA with high molecular weight and/or high A + T content, as also observed with H1. The presence of 6 M urea in the assay mixture does not impair the selectivity of H5 to A + T rich DNA but partly affects its selectivity to DNA size. In contrast to H1, H5 does not discriminate between the superhelical and relaxed forms of circular SV40 DNA.

Histones H1 and H5 interact preferentially with crossovers of double-helical DNA.

“…6). While direct competition experiments confirmed the claimed preference for superhelical DNA molecules in the case of Hi (11,12) and H10 (12), the issue of whether histone H5 [the Hi variant specific to nucleated erythrocytes (13, 14)] possesses such a property is still a matter of controversy (11,15).Previous studies of this phenomenon are subject to a general criticism. In most cases plasmid or viral DNA preparations were used that were poorly characterized with respect to their topological state.…”

Interaction of histones H1 and H1° with superhelical and linear DNA

“…The results of the direct competition experiments performed in this study show that: (i) Hl possesses a strong binding preference for supercoiled DNA forms as compared with their linear counterparts of the same molecular mass; and (ii) histone Hl", in contrast to H5 [4], is indistinguishable with respect to its preference for supercoiled DNA. These facts mean that the functional differences observed between Hl and Hl" do not involve different affinities of the proteins to differently supercoiled DNA, constrained in the distinct loop domains of the eukaryotic genome.…”

“…Thus, for instance, Knippers et al [3] considered the apparent preference for supercoiled DNA as a consequence of the fact that at the ionic strength at which the original experiments of Vogel and Singer were performed (100 mM NaCl), the cooperativity of binding of Hl to DNA was lowered by the superhelicity of DNA which led to retention of more supercoiled molecules on the filters. Iovcheva and Dessev [4] also argued that the efficiency of complex formation between histone and difThe aim of our work was to reinvestigate the binding of Hl to superhelical and linear DNA forms by the use of direct competition experiments. In addition, we compared the behavior of Hl', the differentiationspecific subfraction of Hl [6-81 with that of Hl.…”

“…ferent forms of DNA could not serve as a reliable measure of affinity under the conditions used. It is clear that in order to distinguish any preference that Hl may have for one form of DNA over the other, direct competition experiments are needed [5] of the kind performed by Iovcheva and Dessev [4].…”