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Biomedical subjects

C Zimmer

Publications and source records attributed to C Zimmer.

At least 163 records · Page 9Linked to original sources
PubMed1979

Structural transitions of chromatin induced by netropsin.

Structural changes of chromatin induced by interaction of netropsin (Nt) with DNA has been examined by analysis of CD and electromicroscopic measurements. The results demonstrate the existence of a transition from the condensed globular state of chromatin into nucleosomal fibres generated by extremely low Nt concentration up to 1 mole Nt per 200 nucleotides. A second transition occurs at high Nt ratio per DNA phosphate (v' = 0.3). involving disorganization of nucleosomal particles. The interference of the Nt binding with chromatin proteins maintaining the sub- and superstructure will be discussed.

Animals↗
PubMed1979

Thymidine photoproducts of non-cyclobutane type as a crucial event in the conformation of UV-irradiated DNA.

The UV-light induced conformational effects in deoxyoligonucleotides and polynucleotides have been analyzed by CD measurements and isolation of the photoproducts. The results demonstrate that the essential photoproduct formed on irradiation of thymidylyl-thymidine at 254 nm is of non-cyclobutane type and may be correlated to the primary photoproduct formed in DNAs at low doses Formation of thymine dimers of cyclobutane-type structure appears to be a secondary product generated by treatment with formic acid.

Chromatography, Paper↗
PubMed1977

Specific interactions of distamycin A and its analogs with (A-T) rich and (G-C) rich duplex regions of DNA and deoxypolynucleotides.

The specific interaction of distamycin A and analogs with DNA's and synthetic deoxypolynucleotide duplexes were studied in detail by means of circular dichroism and the data were analyzed together with viscosity results of several natural DNA's. At low ligand to nucleotide ratio the previously reported specific binding to (A-T) pairs of DNA is verified by a highly favoured interaction with (A-T)-enriched segments of distamycins containing four and five methylpyrrole carboxamide units. At higher distamycin concentration a second specific binding to (G-C) pairs most probably through hydrogen bonding is established. Viscometric results suggest a distamycin-induced local bending of the helix and could support the idea of a preferential alignment of the ligand molecule along only one strand in the groove which differs from the netropsin interaction mechanism. The possibility of an overlapping binding of the oligopeptides in the small groove is discussed.

Animals↗
PubMed1976

Conformational changes of nucleic acids and poly (d(A-T)-d(A-T)) caused by photoaddition of furocoumarins.

DNA's of various AT content, poly[d(A-T)-d(A-T)], and double-stranded RNA were irradiated with UV light at 365 nm in the presence of linear (xanthotoxin) or angular (angelicin) furocoumarins. The covalent photobinding is strongly dependent on the spatial arrangement of furocoumarin molecules at the polymer conformation. CD measurements demonstrate that the bifunctional photochemical binding of xanthotoxin with double-stranded DNA's and poly[d(A-T)-d(A-T)] is accompanied by conformational changes which involve probably decreasing helical twisting of the double helix. This effect is greatly enhanced with increasing AT content. The formation of A-like structures is very unlikely since the B leads to A transition induced by ethanol addition was found to be strongly suppressed in xanthotoxin photoreacted DNA. The B-type helix appears to be the most sensitive conformation with minor restriction to produce photochemically induced cross-links.

Binding Sites↗
PubMed1976

CD studies on the conformation of oligonucleotides complexed with divalent metal ions: interaction of Zn2+ with guanine favours syn conformation.

The interaction of the divalent metal ions Mg2+, Mn2+, Zn2+ and Cu2+ with GpG and several other dinucleoside monophosphates were investigated by means of circular dichroism. The spectra of the complexes of GpG, GpU analogues and ApGpG caused in the presence of Zn2+ and other transition metals show a close similarity in the spectral CD shape to that previously reported in the literature for GpG and GpU at low pH and for m7GpG. From the results it may be concluded that transition metal ions-particularly considered for Zn2+/- tends to favour the degree of stacking with Guo in syn conformation in GpG or GpU due to the coordination of the metal ion at N-7 of the 3'-bound position while shielding of the phosphate site by Mg2+ does not influence the sugar-base torsional angle under comparable conditions. Stereochemical aspects and selectivity of the Zn2+ mediated conformation of the dinucleoside phosphates are discussed.

Cations, Divalent↗
PubMed1976

Basic polypeptides as histone models. Effect of conformation, base composition and methylation of nucleic acids on the interaction with H1 and histone models and on the circular dichroism of complexes.

Interaction of histone H 1 and models simulating histone chains was followed by monitoring the melting curves of supernatants after the sedimentation of aggregated complexes. In a mixture of two DNAs the histones reacted selectively with (A+T)-rich and non-methylated DNA, respectively. H 1 and (Ala-Lys-Pro)n also interacted preferentially with DNA in a mixture with double stranded RNA whereas (Lys30,Ala70)n did not show any selectivity. (G+C)-rich DNA in complexes showed CD spectra the intensity of which decreased with increasing DNA methylation to values comparable with these of complexes of (A+T)-rich DNA. In complexed with double stranded RNA only the polymer (Lys30,Ala70) displayed CD pattern similar to spectra of complexes with DNA. It was concluded that formation and structure of complexes depend selectively on the DNA conformation and base composition.

Binding Sites↗
PubMed1976

Conformation and reactivity of DNA in the complex with proteins. III. Helix-coil transition and conformational studies of model complexes of DNA's with poly-L-histidine.

Differences in the interaction of poly-L-histidine with DNA of various base composition have been demonstrated using melting and CD measurements. The two types of complexes formed with DNA at pH values below the pK of 5.9 and in the region of pH 6.5 are very different in their CD spectral properties. The binding effects with highly protonated poly-L-histidine are AT-dependent as reflected by large negative CD spectra indicating the formation of psi-DNA as a condensed state of the double helix. GC-rich DNA may, however, also form psi-DNA structures with poly-L-histidine under certain conditions. At pH 6.5 complex formation with the weakly protonated polypeptide is GC-dependent. From the results it is concluded that protonated poly-L-histidine interacts more specifically at AT base pairs, prabably along the small groove while the weakly protonated poly-L-histidine tends to interact preferentially with GC regions which seems to occur rather in the large groove.

Binding Sites↗
PubMed1976

Duplex structure formation between oligo(dA)'s and oligo(dT)'s generated by thymine-specific interaction with netropsin.

The formation of oligomeric duplex molecules in the presence of the antibiotic netropsin in the series p(dA)n-p(dT)n is demonstrated using low-temperature CD measurements. Addition of Netropsin to mixtures of oligomers generates the same type of CD spectra as observed for poly(dA)-poly(dT) and maintains the duplex structure at temperatures at which base pairing of free oligomers is thermodynamically unstable. The shortest chain length forming a netropsin complex by thymine-specific interaction with the oligopeptide is represented by p(dA)4-p(dt)4. Studies with sequence isomers show that adjacent thymine residues strongly favour the complex formation with the oligopeptide.

Adenine Nucleotides↗
PubMed1974

Conformation dependent binding of netropsin and distamycin to DNA and DNA model polymers.

The binding of the antibiotics netropsin and distamycin A to DNA has been studied by thermal melting, CD and sedimentation analysis. Netropsin binds strongly at antibiotic/nucleotide ratios up to at least 0.05. CD spectra obtained using DNA model polymers reveal that netropsin binds tightly to poly (dA) . poly (dT), poly (dA-dT) . poly(dA-dT) and poly (dI-dC) . poly (dI-dC) but poorly, if at all, to poly (dG) . poly (dC). Binding curves obtained with calf thymus DNA reveal one netropsin-binding site per 6.0 nucleotides (K(a)=2.9 . 10(5) M(-1)); corresponding values for distamycin A are one site per 6.1 nucleotides with K(a)= 11.6 . 10(5) M(-1). Binding sites apparently involve predominantly A.T-rich sequences whose specific conformation determines their high affinity for the two antibiotics. It is suggested that the binding is stabilized primarily by hydrogen bonding and electrostatic interactions probably in the narrow groove of the DNA helix, but without intercalation. Any local structural deformation of the helix does not involve unwinding greater than approximately 3 degrees per bound antibiotic molecule.

Animals↗