Biomedical subjects

M Daune

Publications and source records attributed to M Daune.

32 records · Page 2Linked to original sources

PubMed1976

Circular dichroism as a probe of DNA structure inside reconstituted nucleohistones.

Reconstituted nucleohistones were obtained by mixing in given conditions acid extracted histones and eukaryotic DNA. The histone/DNA ratio (w/w) was in the range 0.35 - 0.95. With the four histones (H2A2B) we have been able to obtain subunits (nucleosomes or upsilon-bodies). The variation of cirsular dichroism signal with temperature at 280 nm was measured to follow structural changes of the DNA inside the complex. The true change of ellipticity (see article) of histone-bound DNA regions, is similar for reconstituted nucleohistone and H1-depleted chromatin, and is therefore a physical probe of the presence of nucleosomes.

Animals↗

PubMed1975

Interaction between hydroxystilbamidine and DNA. I. Binding isotherms and thermodynamics of the association.

Isotherms describing the binding of hydroxystilbamidine to DNA and polydeoxyribonucleotides were obtained by means of sedimentation or dialysis experiments and fluorescence measurements, over a large range of ionic strengths, temperatures and base compositions. Two different sets of binding sites are necessary to explain the shapes of the isotherms. The first one is characterized by a higher binding constant, a topological specificity for the A-T pair, exclusion of four base pairs per bound dye molecule, the involvement of two ion-pairs, an almost purely entropic free energy of binding and a large enhancement of the blue fluorescence (450 nm) when the site corresponds to three adjacent A-T pairs. The latter does not present any specificity nor enhancement of fluorescence and only one ion-pair is formed. From the geometry of the dye and its selective binding to a double stranded structure, the hydroxystilbamidine molecule in the first set of sites is likely to be situated in the small groove astride the two complementary strands and slightly distorting the helical structure. The angle of the dye axis with the helix axis has a value close to 47 degrees. No definite explanation could be given for the specific binding of hydroxystilbamidine but the phenolic hydroxyl group is likely to play a major role. The hydroxystilbamidine molecule can be considered as a useful tool for checking the accessibility of the small groove.

Binding Sites↗

PubMed1975

Interaction between hydroxystilbamidine and DNA. II. Temperature jump relaxation study. Dynamics of nucleic acids and polynucleotides.

A temperature-jump relaxation study of the interaction of hydroxystilbamidine with DNA and synthetic polynucleotides has been performed. Two concentration dependent relaxation times tau1 and tau2 have been observed in the submillisecond range when detecting relaxation effects by means of light absorption. The longer of these two times (tau1) is also observed when using "blue" or "red" fluorescence detection. In the longer time scale the "red" fluorescence shows no other relaxation but the blue fluorescence shows two additional relaxation processes (tau3 and tau4) which correspond to an increase of fluorescence with temperature and which are independent of concentration. The experimental results clearly indicate that tau1 and tau2 are associated with the binding of the dye to strong and weak binding sites, respectively. A kinetic model is given to explain the results. It allows the determination of the four rate constants for the two binding reactions and yields equilibrium association constants in good agreement with those obtained from stoichiometric studies. The study of the effect of temperature, nature of the polymer, ionic strength and fraction of bound dye on tau3 and tau4 indicates that the dye acts only as a "blue" fluorescence probe of some processes involving the DNA or polynucleotide alone. These processes appear to be related with the dynamic structure of the polymers.

Animals↗

PubMed1975

Comparison between histones FV and F2a2 of chicken erythrocyte. I. Structure, stability and conformation of the free proteins.

Purified chicken erythrocyte histones FV and F2a2 were studied by means of circular dichroism as a function of ionic strength and temperature. The percentage of alpha-helical regions was calculated by comparison with reference spectra obtained with four standard proteins of known tertiary structure. Maximal alpha-helical organization, reached in high ionic strength, was estimated to 14% and 23% for FV and F2a2 respectively. We have compared our experimental determinations of the secondary structure of F2a2 with predictions made from amino-acid sequence according to Fasman's rules. When instability induced by the presence of charged residues close together is taken into account, a good agreement is found between predicted and observed values. The thermal denaturation of FV is cooperative and, unlike F2a2, seems to obey a two-state transition. The classical Arrhenius plot is linear, which indicates that the heat capacity is the same in both the native and the denatured state. Such a behaviour is typical of an expanded configuration of FV even in the "native" state.

Amino Acids↗

PubMed1975

Comparison between histones FV and F2a2 of chicken erythrocyte. II. Interaction with homologous DNA.

The conformation and stability of artificial complexes between chicken erythrocyte DNA and homologous histones FV and F2a2 was studied by circular dichroism (CD) and thermal denaturation followed by both absorbance and CD measurements. The complexes are made after a stepwise potassium fluoride gradient dialysis without urea and studied at low ionic strength (10-minus 3 M). 1) No structural changes of the DNA can be detected up to r equals 0.2 with FV and r equals 0.6 for F2a2. With FV at higher values of r the CD spectrum is altered, indicating the organization of DNA and histones in some kind of aggregate. 2) The conformation of histone molecules inside the complexes is not related to the ionic strength of the medium but to an effective ionic environment close to 0.1 M. This ionic strength would also correspond to the melting temperature of histone-covered DNA. 3) From the analysis of the absorbance melting profile the length of DNA covered with an histone molecule can be estimated. A good agreement is found between the negative charge of this piece of DNA and the net positive charge of the histone. 4) Since the CD transition at 227 nm occurs before the second absorbance transition at 280 nm, the DNA is stabilized no longer by native histone but partially or fully denatured histones. The helical regions of the histone molecule are not involved in the binding process, which appears to be almost purely coulombian and most likely related to some structural fit between the pattern of negative charges in the DNA helix and that of positive charges along the peptide chain.

Animals↗

PubMed1974