Condensation and precipitation of chromatin by multivalent cations.

The condensation and the precipitation of rat liver chromatin upon addition of spermine4+, spermidine3+, hexamminecobalt(III)3+ and Mg2+ cations have been studied using solubility, fluorescence, circular dichroism, melting curves, electric dichroism and spermidine binding measurements, made on both soluble and precipitated complexes. The soluble complexes obtained with tetra- and trivalent cations were depleted from all histones and enriched in other proteins, particularly high mobility group proteins 1 and 2, which brings about an important enhancement of tryptophan fluorescence without modification of its two lifetimes 5.1 and 1.

An electro-optical study of the mechanisms of DNA condensation induced by spermine.

Condensation of DNA by spermine has been studied by electric dichroism, electric birefringence and rotational relaxation times at 1 mM ionic strength. Using Manning's theory, we found that condensation occurs for a fraction of neutralized phosphate charges (r) equal to 0.90, in good agreement with previous studies using spermidine, synthetic polyamines and trivalent cations (e.

Activation of cytosol aldosterone receptors in rat kidney.

Cytosolic aldosterone-protein complexes are isolated from rat kidney slices after incubation with [3H]aldosterone and dexamethasone. Activated and unactivated forms of the complex are characterized by gel electrophoresis and hydroxyapatite chromatography after incubation at 4 degrees C and 25 degrees C respectively. It is found that the activated form reaches a maximum after 30 min at 25 degrees C and can be separated as an homogeneous peak by electrophoresis.

Terbium(3+) as a probe of nucleic acids structure. Does it alter the DNA conformation in solution?

At low ionic strength, Tb3+ binding strongly alters the secondary structure of DNA. Circular dichroism and electro-optical techniques are more sensitive than fluorescence to study these alterations in double-stranded DNA, at low Tb3+/DNA phosphate (I/P) ratios. Both techniques yield the following conclusion: as I/P is increased, native and sonicated DNA undergo a transition from the B- to psi-form, the latter being a compact structure characteristic of aggregated DNA.

Alteration in the nucleosome and chromatin structures upon interaction with platinum coordination complexes.

The interaction of various platinum coordination complexes with nucleosomes and chromatin has been investigated by ultraviolet absorption spectrophotometry, circular and electric linear dichroism, and thermal denaturation, at low binding ratios (r less than 0.1-0.2).

Denaturation level of DNA-Pt complexes evidenced by Tb3+ fluorescence enhancement and electric dichroism.

The Tb3+ fluorescence is greatly enhanced, as a result of binding of various platinum coordination complexes to DNA, as compared to native DNA. The largest enhancement is observed for cis-Pt(NH3)2Cl2 but the fluorescence intensity does not however reach the level attained for thermally denatured DNA. Diethylenetriamine-Pt(II) produces very little increase of Tb3+ fluorescence.

[Effects of cis-dichlorodiaminoplatinum II (cis-Pt II) on chromatin ultrastructure in animal or plant cells and repercussions on the cell cycle].

Cultivated animal cells (mouse peritoneal macrophages, chick fibroblasts or mouse Ehrlich tumor cells) or Zea mays root tips are treated with cis-Pt (II). Various effects (chromatin dispersion or condensation, pycnosis) are observed under some experimental conditions in all cell types. Cytoplasmic ribosomes in helical aggregates appear but only in vegetal cells.

Electric birefringence of DNA and chromatin. Influence of divalent cations.

The effects of divalent cations on the DNA and chromatin conformation have been investigated by electric birefringence and birefringence relaxation measurements at low and constant ionic strength (0.001). An important decrease of the intrinsic optical anisotropy of DNA has been found in the presence of Mn2+ and Cu2+, but not with Mg2+.

Interaction of DNA and purine nucleosides with cis-dichlorodiammineplatinum(II) and antimitotic activity of the complexes on meristematic root cells.

The appropriate experimental conditions for the preparation of complexes of cis-dichlorodiammineplatinum(II) with DNA and with purine nucleosides have been determined which leave negligible amounts of free drug in the solution. Important conformational changes of DNA upon binding to cis-Pt(NH3)2-Cl2 have been evidenced through viscosity, electric birefringence and thermal denaturation experiments. The antimitotic and antitumor activity of the drug was found to be totally inhibited by its binding to DNA and to the purine nucleosides.

The role of the AT pairs in the acid denaturation of DNA.

It has been determined previously that the protonation of the GC pairs induces a DNA conformation change which leads to a "metastable" structure. The role of the AT pairs, however, is no well known because the protonation does not modify their spectral properties. By means of an indirect method based on the binding of proflavine, it has been determined that the AT pairs are protonated before the acid-induced denaturation and that they seem to be unable to assume a conformation change when protonated.

Interaction of ethidium bromide with ribosomes. Absorption, fluorescence, circular dichroism and sedimentation studies.

It is shown in this work that the binding of ethidium bromide to yeast ribosomes occurs through intercalation in the double-stranded rRNA regions and produces changes in the ribosomes structure, yielding unfolded subparticles, and even partial separation of proteins from rRNA at very high binding ratios. The addition of Mg2+ prevents these structural changes, probably by partial inhibition of the dye binding.

Binding of ethidium bromide to ribosomal RNA. Absorption, fluorescence, circular and electric dichroism study.

The interaction between ethidium bromide and ribosomal RNA has been studied by means of absorption, fluorescence, circular and electric dichroism measurements in the near ultraviolet and visible regions at low ionic strength (1 . 10(-3) and 6 . 10(-3).

Physico-chemical study of the complexes of "33258 Hoechst" with DNA and nucleohistone.

The degree of binding of "33258 Hoechst" to DNA and nucleohistone has been determined by equilibrium dialysis and the properties of the complexes have been followed by different optical and electro-optical methods, after determining the orientation of the main transition moments within the dye molecule. The binding isotherm was found composed of a Langmuir-type and of a strongly cooperative component. The existence of two bound species yielded a continuous variation of most of the properties of the complexes studied as the amount of binding increased, while the hydrodynamic properties of the macromolecules were not affected.

Preparation and some properties of strongly acidic proteins from calf-thymus nucleohistone.

The isolation of acidic proteins from calf-thymus nucleohistone (starting from purified nuclei) is reported. The method involved dissociation in 1 M KCl solution. Denaturating agents were not used at all.