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J Sponar

Publications and source records attributed to J Sponar.

35 records · Page 2Linked to original sources
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↗
PubMed1975

Cyclization of three satellite components of calf thymus DNA.

Cyclization of denatured and reannealed satellite components of calf thymus DNA was studied by electron microscopy. All three satellite DNA components studied (1.707g/cm-3, 1.714g/cm-3 and 1.721g/cm-3) form circular structures indicating that the sequences of the calf thymus satellite DNAs are arranged in a tandemly repetitious manner. Under appropriate annealing conditions the amount of circular structures is reproducible and practically no aggregates are formed. By comparison of cyclization experiments under defined conditions it is demonstrated that individual satellite components differ in the amount of circular structures formed during reassociation and in the distribution of linear and circular molecules. From the distribution of the contour lengths of circular molecules we conclude that the length of the repetitive sequence decreases with increasing buoyant density of the satellite components. The average lengths of the repetitive sequences calculated from electron microscopy measurements are in good agreement with those from renaturation kinetics.

Animals↗
PubMed1975

Basic polypeptides as histone models: circular dichroism of complexes of model polypeptides with DNA.

Circular dichroism (CD) was used to study the complexes of DNA (in 0.15M NaCl) with two polypeptides considered as models of the histone molecules. CD spectra in the region of DNA absorption were studied with respect to the concentration used for annealing and to the molecular weight and composition of the DNA used. The properties of supernatants after centrifugation of aggregated complexes were examined. The effect of selectively bound antibiotics (actinomycin D and netropsin) on CD sprectra of complexes was investigated. The induced CD of proflavine molecules bound to DNA in the various complexes was also studied. It was concluded that changes in the CD spectra of DNA in complexes with the polypeptides are due to the formation of chiral superstructures, even if some conformational changes of DNA molecules themselves may also be decisive in some cases. The superstructure is affected by the composition of DNA, the role of (G + C) rich segments being particularly important.

Binding Sites↗
PubMed1975

Reassociation kinetics of three satellite components of calf thymus DNA.

Using absorption measurements the reassociation kinetics of three satellite DNA components isolated from calf thymus was studied under various conditions. A different method using CsC1 density gradient determinations particularly suited for kinetic analysis of mixtures was also used and shown to give similar results. Reassociation rate constants were corrected for mismatching during strand reassociation using data obtained by kinetic analysis of fractions of the 1.714 g/cm-3 satellite component. The values of corrected as well as uncorrected complexities were calculated and compared with results of other methods. They were shown to be compatible with the concept of sequence repetition at various levels.

Animals↗
PubMed1975

Identification and separation of components of calf thymus DNA using a CsC1-netropsin density gradient.

Calf thymus DNA containing satellite components of various densities was used as a model to study the effect of netropsin on the density of DNA in a CsCl gradient. The binding of netropsin resulted in a decrease in density which depended upon the quantity of netropsin added and on the average composition of the DNA. Differences in density of DNA components were higher in CsCl - netropsin gradients than in simple CsCl gradients. By use of netropsin a main band and four satellite bands could be differentiated in calf thymus DNA. Satellite DNA's were isolated using preparativeCsCl - netropsin gradient centrifugation and were characterised by density and homogeneity in native and in reassociated state. Two of the satellite components, with densities of 1.722 and 1.714 g/cm minus 3, are probably of homogenous sequence, the other two components of densities 1.709 and 1.705 g/cm minus 3 appear to be heterogeneous.

Animals↗
PubMed1974

Structural transitions of polyadenylic acid due to protonation: the influence of the length of single strands on the polarographic behaviour of the double-helical form.

Transition of single-stranded poly(A) into its double-helical protonated form was followed by means of derivative pulse polarography, spectrophotometry, and other methods. It was found that properties of protonated poly(A) depended on the length of single strands from which the protonated double helix was formed. In contrary to longer poly(A) transition of short single-stranded molecules (s(20),w lower than about 3) caused practically no decrease in the pulse-polarographic current. It was concluded that the formation of the protonated double helix of poly(A) did not result in the inaccesibility of the reduction sites (located in the vicinity of the surface of the molecule) for the electrode process, as it was in DNA-like double-helical polynucleotides. The current changes observed in the course of transition of longer poly(A) were explained as due to slower transport of long double-stranded molecules to the electrode.

Nucleic Acid Conformation↗
PubMedDate not supplied

[Design and synthesis of peptides capable of specific binding to DNA].

In the present communication, design, synthesis and DNA binding activities of the following two peptides are reported: Dns-Gly-Ala-Gln-Lys-Leu-Ala-Cly-Lys-Val-Gly-Thr-Lys-Val-Lys-Val-Gl y-Thr-Lys-Thr - Val-OH (I) and [(H-Ala-Lys-Leu-Ala-Thr-Lys-Ala-Gly-Val-Lys-Gln-Gln-Ser-Ile-Gln-Leu-Ile- Thr- Ala-Aca-Lys-Aca)2Lys-Aca]2Lys-Val-OH (II), where Aca = NH(CH2)5CO--; Dns is a residue of 5-dimethylaminonaphtalene-1-sulfonic acid. Peptide I contains a large fraction (ca.30%) of valyl and threonyl residues, which possess a high potential for beta structure formation. Peptide II contains four repeats of the amino acid sequence present in the presumed DNA binding helix-turn-helix unit of 434 Cro repressor. These four domains are linked in such a way that two domains can interact with two halves a 14 base pair long operator site on DNA. From CD studies we have found that peptide I is in a random coil conformation in the aqueous solution in the presence of 20% trifluoroethanol. By contrast, amino acid residues of peptide II assume alpha helical, beta and random coiled conformations under the same conditions. A change in the secondary structure of the two peptides upon binding to DNA is observed. The difference CD spectra obtained by subtracting the spectra of free DNA from the spectra of peptide I--DNA complexes gives rise to a beta-like pattern. The difference CD spectra obtained for complexes of peptide II with various natural and synthetic DNAs suggest that alpha-beta-transition takes place in the presumed helix-turn-helix repeat units of peptide II upon binding to DNA. Peptide I binds more strongly to poly(dG).poly(dC) than to poly(dA).poly(dT) and poly[d(GC)].poly[d(GC)]. The binding takes place in the minor DNA groove because minor groove binding antibiotic sibiromycin can displace peptide I from a complex with poly(dG).poly(dC). Analysis of footprinting diagramms shows that peptide I specifically protects phosphodiester bonds within operator sites OR1 and OR2 of phage lambda from nuclease cleavage. By contrast, peptide II does not react specifically with operators OR1, OR2 and OR3 of phage 434 although it forms very tight complexes with DNA which are stable in the presence of 1M NH4F.

Animals↗