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PubMed2004

Poly(D,L-lactide-ran-epsilon-caprolactone)-poly(ethylene glycol)-poly(D,L-lactide-ran-epsilon-caprolactone) as parenteral drug-delivery systems.

P(DLAX-ran-CLY)n-b-PEG-b-P(DLAX-ran-CLY)ns (P(DLAX-ran-CLY)m: Poly(d,l-lactide-ran-epsilon-caprolactone), PEG: Poly(ethylene glycol), X: d,l-lactyl unit ratio, Y: epsilon-caproyl unit ratio, m : molecular weight of P(DLAX-ran-CLY)), were investigated as the novel parenteral drug-delivery system. The thermal behavior in the DSC characterization and variable viscosity with temperature suggest their potential usuage as a injectable drug-delivery system. The variation of tri-block structure affects the drug release behavior by changing the morphology and also by changing the interaction between the polymer matrix and the hydrophilic drug.

Biocompatible Materials↗

PubMed2005

The effect of epsilon-caproyl/D,L-lactyl unit composition on the hydrolytic degradation of poly(D,L-lactide-ran-epsilon-caprolactone)-poly(ethylene glycol)-poly(D,L-lactide-ran-epsilon-caprolactone).

The degradation of P(DLAX-ran-CLY)-b-PEG-b-P(DLAX-ran-CLY)s ( P(DLAX-ran-CLY): Poly(D,L-lactide-ran-epsilon-caprolactone), PEG: Poly(ethylene glycol), X: D,L-lactyl unit fraction, Y: epsilon-caproyl unit fraction) is investigated. The fraction of DLA in the both end blocks is varied while the overall molecular weight and molecular weight of PEG are kept constant. DSC, XRD and GPC are employed to track the degradation process up to 200 days. Also the change in the surface and cross-sectional morphology is provided by SEM micro-photographs. The result of water absorption and weight loss characterization reveals that the incorporation of DLA in the polyester block could be an effective tool to facilitate degradation as well as water absorption. By tracking the change of molecular weight and polydispersity, chain scission and transport or removal of degraded product from the specimen were found to play a complex role in overall degradation.

Absorption↗

PubMed2004

Temperature and concentration effects on supramolecular aggregation and phase behavior for poly(propylene oxide)-b-poly(ethylene oxide)- b-poly(propylene oxide) copolymers of different composition in aqueous mixtures, 1.

The phase behavior (temperature vs composition) and microstructure for the two binary systems Pluronic 25R4 [(PO)19(EO)33(PO)19]-water and Pluronic 25R2 [(PO)21(EO)14(PO)21]-water have been studied by a combined experimental approach in the whole concentration range and from 5 to 80 degrees C. The general phase behavior has been identified by inspection under polarized light. Precise phase boundaries have been determined by analyzing 2H NMR line shape. The identification and microstructural characterization of the liquid crystalline phases have been achieved using small-angle X-ray scattering (SAXS). The isotropic liquid solution phases have been investigated by self-diffusion measurements (PGSE-NMR method). 25R2 does not form liquid crystals and is miscible with water in the whole concentration range; with increasing temperature, the mixtures split into water-rich and a copolymer-rich solutions in equilibrium. 25R4 shows rich phase behavior, passing, with increasing copolymer concentration, from a water-rich solution to a lamellar and copolymer-rich solution. A small hexagonal phase, completely encircled in the stability region of the water-rich solution, is also present. In water-rich solutions, at low temperatures and low copolymer concentrations, the copolymers are dissolved as independent macromolecules. With increasing copolymer concentrations an interconnected network of micelles is formed in which micellar cores of hydrophobic poly(propylene oxide) are interconnected by poly(ethylene oxide) strands. In copolymer-rich solutions water is molecularly dissolved in the copolymer. The factors influencing the self-aggregation of Pluronic R copolymers (PPO-PEO-PPO sequence) are discussed, and their behavior in water is compared to that of Pluronic copolymers (PEO-PPO-PEO sequence).

Macromolecular Substances↗

PubMed2004

In vivo and in vitro degradation of poly(ether ester) block copolymers based on poly(ethylene glycol) and poly(butylene terephthalate).

Two in vivo degradation studies were performed on segmented poly(ether ester)s based on polyethylene glycol (PEG) and poly(butylene terephthalate) (PBT) (PEOT/PBT). In a first series of experiments, the in vivo degradation of melt-pressed discs of different copolymer compositions were followed up for 24 weeks after subcutaneous implantation in rats. The second series of experiments aimed to simulate long-term in vivo degradation. For this, PEOT/PBT samples were pre-degraded in phosphate buffer saline (PBS) at 100 degrees C and subsequently implanted. In both series, explanted materials were characterized by intrinsic viscosity measurements, mass loss, proton nuclear magnetic resonance spectroscopy (1H-NMR) and differential scanning calorimetry (DSC). In both studies the copolymer with the higher PEO content degraded the fastest, although all materials degraded relatively slowly. To determine the nature of the degradation products formed during hydrolysis of the copolymers, 1000 PEOT71PBT29 (a copolymer based on PEG with a molecular weight of 1000 g/mol and 71 wt% of PEO-containing soft segments) was degraded in vitro at 100 degrees C in phosphate buffer saline (PBS) during 14 days. The degradation products present in PBS were analyzed by 1H-NMR and high performance liquid chromatography/mass spectroscopy (HPLC/MS). These degradation products consisted of a fraction with high contents of PEO that was soluble in PBS and a PEOT/PBT fraction that was insoluble at room temperature. From the different in vitro and in vivo degradation experiments performed, it can be concluded that PEOT/PBT degradation is a slow process and generates insoluble polymeric residues with high PBT contents.

Animals↗

PubMed2001

Fractionation of functional polystyrenes, poly(ethylene oxide)s and poly(styrene)-b-poly(ethylene oxide) by liquid chromatography at the exclusion-adsorption transition point.

The paper reports the fractionation of functional polystyrenes (PSs) and poly(ethylene oxide)s (PEOs) as well as their block copolymers, by liquid chromatography at the exclusion adsorption transition point (EATP-LC), also called "critical conditions" mode. In this specific elution mode (EATP-LC), the fractionation is only governed by the nature and the number of functions attached to the polymer backbone, independent of the molar mass distribution of the whole sample. Functional polystyrenes (alpha- and/or alpha,omega-alcohol-, acetal-, aldehyde- and acidic-PS) could be readily separated from non-functional polystyrenes under various chromatographic conditions. The technique also allowed the fractionation of poly(ethylene oxide)s and PS-PEO block copolymers. In the latter cases, moderately polar columns (grafted silica) and water-based polar eluents were required to obtain a satisfactory fractionation.

Adsorption↗

PubMed1997

Differences between dynamic and equilibrium surface tension of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymer surfactants (poloxamers P407, P237, and P338) in aqueous solution.

Poloxamer surfactants are macromolecules with complex interfacial behavior. Although a number of studies of equilibrium surface tension have been published recently, there is little information on the diffusion of these large molecules to the air-liquid interface. Because most surfactants are used in dynamic systems, the diffusion to the surface can be critical in controlling performance. In this study a maximum bubble pressure method was used to study dynamic surface tension (DST) of Poloxamer P407, P237, and P338, at a range of bubble rates (surface age) and concentrations, at either 25 or 35 degrees C. The DST did not change at the critical micelle concentration and also did not vary in the same manner as the equilibrium surface tension (EST) with respect to temperature. It was concluded that DST behavior of the surfactants was most closely related to the poly(oxyethylene) content and/or total molecular weight of the surfactants, whereas the micellization and hence the EST were more closely related to the poly(oxypropylene) content.

Poloxalene↗

PubMed1980

Elicitation of delayed-type hypersensitivity responses to poly(L-Tyr,LGlu)-poly(DLAla)--poly(LLys) by anti-idiotypic antibodies.

The in vivo effect of murine anti-idiotypic serum against C3H.SW anti-poly(LTyr,LGlu)-poly(DLAla)-(LLys) [(T,G)-A--L] antibodies on delayed type hypersensitivity responses to (T,G)-A--L was studied. Anti-idiotypic serum could challenge DTH responses in C3H.SW mice transferred with antigen-sensitized T cells. The elicitation activity was shown to be antigen and strain specific. With H-2-compatible (but allotype different) strain combinations of (T,G)-A--L-educated T cells and recipients, we were able to show that the biological effect of the anti-idiotypic serum is expressed on the first antigen-sensitized idiotype-positive radioresistant T cell, but not on the proliferating normal cells of recipient origin that participate in the efferent phase of delayed-type hypersensitivity responses to (T,G)-A--L.

Animals↗

PubMed2003

Out of equilibrium dynamics of poly(vinyl methyl ether) segments in miscible poly(styrene)-poly(vinyl methyl ether) blends.

The local dynamics of the low-T(g) component in a polymer blend, dynamically asymmetric poly(styrene)-poly(vinyl methyl ether) (PS-PVME), is studied below the glass transition, via dielectric relaxation spectroscopy. A particular attention has been paid to blends with a high PS content (PS weight fraction higher than 50%). A relaxation process, slower than the localized motions inducing the PVME secondary relaxations, is detected. Even though these blends fall out of equilibrium in this temperature regime, the structural recovery process is not efficient on the time scale of this PVME motional process. This relaxation is attributed to rather localized, weakly cooperative PVME motions resulting from the topological constraints imposed by the frozen PS chains.

Journal Article↗

PubMed1976

Role of purine N-3 in the biologic activities of poly(A) and poly(I).

Poly(c3A) (poly 3-deazaadenylic acid) and poly(c3I) (poly 3-deazainosinic acid) differ in biological reactivity from their parent compounds poly(A) and poly(I) and from their 7-deaza counterparts poly(c7A) and poly(c7I). Three parameters of biological reactivity were evaluated : (1 degree) interferon induction, (2 degrees) anti-complement activity, (3 degrees) reverse transcriptase inhibition. Unlike poly(A)-poly(U), poly(I)-poly(C) and poly(I)-poly(br5C), the mixtures of poly(c3A) + POLY(U), poly(c3I) + poly(C), and poly(c3I) + poly(br5C) failed to elicit an interferon response in "super-induced" primary rabbit kidney cells; Poly(I) and its analogs poly(c3I) and poly(c7I) inhibited hemolytic complement activity, whereas poly(A) and its analogs poly(c3A) and poly(c7A) failed to do so. Both poly(I) and poly(c7I), but not poly(c3I), lost their anti-complement potency when annealed to either poly(C) or poly(A)-poly(U). Similarly, poly(I) and poly(c7I), but not poly(c3I), suppressed the interferon inducing ability of poly(A)-poly(U), suggesting that both poly(I) and poly(c7I), but not poly(c3I), added to poly(A)-poly(U) to form a triple-helical structure. Poly(I), poly(C7I) and poly(c7A)exerted a distinct inhibitory effect on turine leukemia virus, while under the same conditions poly(c3I) and poly(c3A) showed little, if any, inhibitory effect.

Animals↗

PubMed1984

The mouse immune response to the double stranded polyribonucleotide complex poly(G) . poly(C).

Ten inbred strains of mice were immunized with the double stranded polyribonucleotide complex polyguanylic . polycytidylic acid [poly(G) . poly(C)]. While some immunogenic properties of this duplex were comparable to those of other nucleic acids antigens, differences were also noted. High (SJL/J, BALB/c), low (DBA/2, AKR) and intermediate responders were observed; these differences were not abolished by adsorption of the duplex to MBSA. This pattern of immune response is distinct both from that observed with two other synthetic polyribonucleotide double helices [poly(A) . poly(U) and poly(I) . poly(C)] and with single stranded DNA. The anti-poly(G) . poly(C) activity was localized in the 7S region, whether the sera came from high or low responders, from mice immunized with or without a carrier, after one or several injections. In contrast with anti-poly(A) . poly(U) sera which do not react with poly(G) . poly(C), anti-poly(G) . poly(C) exhibited poly(A) . poly(U) binding activity; no clear relationship between the two activities, however, could be demonstrated. Thus a series of immunological properties differentiates poly(G) . poly(C) not only from the natural polydeoxyribonucleotide single stranded DNA, but also, and more unexpectedly, from two other double stranded polyribonucleotide complexes. These observations suggest that the mechanism controlling the antibody response to poly(G) . poly(C) differs from that regulating poly(A) . poly(U) and/or poly(I) . poly(C), and are to be connected with the fact that the anti-poly(G) . poly(C) antibodies occurring in the sera of patients with systemic lupus erythematosus did not correlate with the antibody activities directed toward the other duplexes.

Animals↗

PubMed1978

Specific binding of poly(I)-poly(C) to the membrane of murine B lymphocyte subsets.

Indirect immunofluorescence revealed that 13% of BALB/c and 33% of CBA spleen cells of B type carry specific binding sites at their surface for double-stranded poly(I).poly(C). Pretreatment of BALB/c spleen cells with anti-mouse immunoglobulin serum increased the number of B cells capable of binding poly(I).poly(C) indicating the existence of a second B lymphocyte subpopulation carrying masked poly(I).poly(C)-binding sites. Pretreatment of the cells with mitogenic doses of either lipopolysaccharide (LPS) or single-stranded polynucleotides, e.g. poly(I) or double-stranded poly(A).poly(U), failed to affect binding of poly(I).poly(C) to the cells. Poly(I).poly(C) converts small poly(I).poly(C)-binding lymphocytes into lymphoblasts carrying poly(I).poly(C)-binding sites. Lymphoblasts derived from LPS-stimulated cells do not carry poly(I).poly(C)-binding sites. Thymocytes or splenic T cells failed to bind poly(I).poly(C). As measured by thymidine uptake, CBA mice containing a higher percentage of poly(I).poly(C)-binding cells, are high responder mice to poly(I).poly(C), compared with low responder BALB/c mice.

Animals↗

PubMed1978

Protonated polynucleotides structures - 22.CD study of the acid-base titration of poly(dG).poly(dC).

The acid-base titration (pH 8 --> pH 2.5 --> pH 8) of eleven mixing curve samples of the poly(dG) plus poly(dC) system has been performed in 0.15 M NaCl. Upon protonation, poly(dG).poly(dC) gives rise to an acid complex, in various amounts according to the origin of the sample. We have established that the hysteresis of the acid-base titration is due to the non-reversible formation of an acid complex, and the liberation of the homopolymers at the end of the acid titration and during the base titration: the homopolymer mixtures remain stable up to pH 7. A 1G:1C stoichiometry appears to be the most probable for the acid complex, a 1G:2C stoichiometry, as found in poly(C(+)).poly(I).poly(C) or poly(C(+)).poly(G).poly(C), cannot be rejected. In the course of this study, evidence has been found that the structural consequences of protonation could be similar for both double stranded poly(dG).poly(dC) and G-C rich DNA's: 1) protonation starts near pH 6, dissociation of the acid complex of poly(dG).poly(dC) and of protonated DNA take place at pH 3; 2) the CD spectrum computed for the acid polymer complex displays a positive peak at 255 nm as found in the acid spectra of DNA's; 3) double stranded poly(dG).poly(dC) embedded in triple-stranded poly(dG).poly(dG).poly(dC) should be in the A-form and appears to be prevented from the proton induced conformational change. The neutral triple stranded poly(dG).poly(dG).poly(dC) appears therefore responsible, although indirectly, for the complexity and variability of the acid titration of poly(dG).poly(dC) samples.

Circular Dichroism↗

PubMed1989

Factor C from rabbit liver. A new poly(dC) and poly[d(G-C)] template-selective stimulatory protein of DNA polymerases.

We have undertaken a search for mammalian DNA-binding proteins that enhance the activity of DNA polymerases in a template sequence-specific fashion. In this paper, we report the extensive purification and characterization of a new DNA-binding protein from rabbit liver that selectively stimulates DNA polymerases to copy synthetic poly[d(G-C)] and the poly(dC) strand of poly(dC).poly(dG) as well as single-stranded natural DNA that contains stretches of oligo(dC). The enhancing protein, a polypeptide of 65 kDa designated factor C, stimulates the copying of the two synthetic templates by Escherichia coli DNA polymerase I, Micrococcus luteus polymerase, and eukaryotic DNA polymerases alpha and beta, but not by avian myeloblastosis virus polymerase. Factor C, however, does not affect utilization by these polymerases of the poly(dG) strand of poly(dC).poly(dG), of poly(dC) primed by oligo(dG), or of poly(dA).poly(dT) and poly[d(A-T)]. With polymerase I, Michaelis constants (Km) of poly[d(G-C)] and of the poly(dC) strand of poly(dC).poly(dG) are decreased by factor C 37- and 4.7-fold, respectively, whereas maximum velocity (Vmax) remains unchanged. By contrast, neither the Km value of the poly(dG) strand of poly(dC).poly(dG) nor the Vmax value with this template is altered by factor C. Rates of copying of activated DNA, denatured DNA, or singly primed M13 DNA are not affected significantly by factor C. However, primer extension analysis of the copying of recombinant M13N4 DNA that contains runs of oligo(dC) within an inserted thymidine kinase gene shows that factor C increases processivity by specifically augmenting the efficiency at which polymerase I traverses the oligo(dC) stretches. Direct binding of factor C to denatured DNA is indicated by retention of the protein-DNA complex on columns of DEAE-cellulose. Binding of factor C to poly[d(G-C)] is demonstrated by the specific adsorption of the enhancing protein to columns of poly[d(G-C)]-Sepharose. We propose that by binding to poly[d(G-C)] and to poly(dC).poly(dG), factor C enables tighter binding of some DNA polymerases to these templates and facilitates enzymatic activity.

Animals↗

PubMed1985

Conformational variability of poly(dA-dT).poly(dA-dT) and some other deoxyribonucleic acids includes a novel type of double helix.

The article reviews data indicating that poly(dA-dT).poly(dA-dT) is able of adopting three distinct double helical structures in solution, of which only the A form conforms to classical notions. The other two structures have dinucleotides as double helical repeats. At low salt concentrations poly(dA-dT).poly(dA-dT) adopts a B-type alternating conformation which is exceptionally variable. Its architecture can gradually move in the limits demarcated by the CD spectra with inverted long wavelength CD bands and the 31P NMR spectra with a very low and a 0.6 ppm separation of two resonances. Contrary to Z-DNA, the 31P NMR spectrum of the limiting alternating B conformation of poly(dA-dT).poly(dA-dT) is characterized by an upfield shift of one resonance. We attribute the exceptional conformational flexibility of the alternating B conformation to the unequal tendency of bases in the dA-dT and dT-dA steps to stack. However, by assuming the limiting alternating B conformation, the variability of the synthetic DNA is not exhausted. Specific agents make it isomerize into another conformation by a fast, two-state mechanism, which is reflected by a further deepening of the negative long wavelength CD band and a downfield shift of the 31P NMR resonance of poly(dA-dT).poly(dA-dT) that was constant in the course of the gradual alterations of the alternating B conformation. These changes are, however, qualitatively different from the way poly(dG-dC).poly(dG-dC) behaves in the course of the B-Z isomerization. Poly(dG-dC).poly(dG-dC) displays purine-pyrimidine (dGpdC) resonance in the characteristic downfield position, while the downfield resonance of poly(dA-dT).poly(dA-dT) belongs to the pyrimidine-purine (dTpdA) phosphodiester linkages. Consequently, phosphodiester linkages in the purine-pyrimidine steps play a similar role in the appearance of the Z form to the pyrimidine-purine phosphodiesters in the course of the isomerization of poly(dA-dT).poly(dA-dT). This excludes that the high-salt structures of poly(dA-dT).poly(dA-dT) and poly(dG-dC).poly(dG-dC) are members of the same conformational family. We call the high-salt conformation of poly(dA-dT).poly(dA-dT) X-DNA. It furthermore follows from the review that synthetic molecules of DNA with alternating purine-pyrimidine sequences of bases can adopt either the Z form or the X form, or even both, depending on the environmental conditions. This introduces a new dimension into the DNA double helix conformational variability. The possible biological relevance of the X form is suggested by experiments with linear molecules of natural DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Cesium↗

PubMed1983

Poly(A) length, cytoplasmic adenylation and synthesis of poly(A)+ RNA in early mouse embryos.

The poly(A) content of early mouse embryos fluctuates widely: after a transient increase in the one-cell embryo, there is a 70% drop in the two-cell and an approximately fivefold increase between the two-cell and early blastocyst stages (L. Pikó and K. B. Clegg, 1982, Dev. Biol. 89, 362-378). To shed light on the significance of these changes, we analyzed the size distribution of total poly(A) from embryos at different stages of development by gel electrophoresis and hybridization with [3H]poly(U). The number-average size of poly(A) tracts varies only slightly, from 61 to 77 nucleotides, indicating that the changes in poly(A) content are due primarily to changes in the number of poly(A) sequences, i.e., the number of poly(A)+ mRNA. From these data, the number of poly(A)+ mRNA can be estimated as follows: ovulated egg, 1.7 x 10(7); one-cell embryo, 2.4 x 10(7); late two-cell, 0.7 x 10(7); late eight-cell, 1.3 x 10(7); and early blastocyst, 3.4 x 10(7). These results suggest the elimination of the bulk of maternal poly(A)+ mRNA at the two-cell stage, to be replaced by newly synthesized mRNA derived from the embryonic genome. To study the synthesis of poly(A)+ mRNA, we cultured mouse embryos in vitro with [3H]adenosine and analyzed the labeled poly(A)+ RNA as to molecular size, length of the poly(A) tail, and relative distribution of label in poly(A) vs internal locations. We observed an active incorporation of label into large-molecular-weight (average size about 2 kb) poly(A)+ RNA at all stages from the one-cell to the blastocyst. However, in the one-cell embryo, about 70% of the label was localized in the poly(A) tail, suggesting cytoplasmic polyadenylation, and only about 30% was localized in the remainder of the molecule, suggesting the complete new synthesis of a small amount of poly(A)+ RNA. Differences in the size distribution of the labeled poly(A) as compared with the total poly(A) in the one-cell embryo indicate that the labeling is not due to a general turnover of poly(A) tails, but rather to the polyadenylation of previously nonpolyadenylated, stored RNA. Significant new synthesis of poly(A)+ RNA is evident from the two-cell stage onward and most likely accounts for the sharp rise in the number of poly(A)+ RNA molecules by the early blastocyst stage.

Adenosine↗

PubMed1984

Solution structure of poly(dA-dT).poly(dA-dT) in low and high salt: a 500 MHz 1H NMR study using one-dimensional NOE.

CD spectra of poly(dA-dT).poly(dA-dT) in low salt (10-100 mM NaCl) and high salt (4-6 M CsF) are different i.e. 275 nm band gets inverted in going from low to high salt (Vorhickova et. al., J. Mol. Biol. 166, 85, 1983). However, from CD spectra alone it is not possible to decipher any structural differences that might exist between the low and high salt forms of poly(dA-dT).poly(dA-dT). Hence, we took recourse to high resolution NMR spectroscopy to understand the structural properties of poly(dA-dT).poly(dA-dT) in low and high salt. A detailed analysis of shielding constants and extensive use of NOE studies under minimum spin diffusion conditions using C(8)-deuterated poly(dA-dT).poly(dA-dT) enabled us to come up with the following conclusions (i) base-pairing is Watson-Crick under low and high salt conditions. (ii) under both the conditions of salt the experimental data can be explained in terms of an equilibrium blend of right and left-handed B-DNA duplexes with the left-handed form 70% and the right-handed 30%. In a 400 base pairs long poly(dA-dT).poly(dA-dT) (as used in this study), equilibrium between right and left-handed helices can also mean the existence of both helical domains in the same molecule with fast interchange between these domains or/and unhindered motion/propagation of these domains along the helix axis. (iii) However, there are other structural differences between the low and high salt forms of poly(dA-dT).poly(dA-dT); under the low salt condition, right- and left-handed B-DNA duplexes have mononucleotide as a structural repeat while under the high salt conditions, right- and left-handed B-DNA duplexes have dinucleotide as a structural repeat. In the text we provide the listing of torsion angles for the low and high salt structural forms. (iv) Salt (CsF) induced structural transition in poly(dA-dT).poly(dA-dT) occurs without any breakage of Watson-Crick pairing. (v) The high salt form of poly(dA-dT).poly(dA-dT) is not the left-handed Z-helix. Although the results above from NMR data are quite unambiguous, a question still remains i.e. what does the salt (CsF) induced change in the CD spectra of poly(dA-dT).poly(dA-dT) really indicate? Interestingly, we could show that the salt (CsF) induced change in poly(dA-dT).poly(dA-dT) is quite similar to that caused by a basic polypeptide viz. poly-L(Lys2-Ala)n i.e. both the agents induced a psi-structure in DNA.

Cesium↗

PubMed1998

Template-dependent biosynthesis of poly(G) x poly (C) and its antiviral activity in vitro and in vivo.

Experimental conditions for poly(G) synthesis from GTP on a poly(C) template with the aid of Escherichia coli DNA-dependent RNA polymerase were investigated. The reaction product was purified without the use of RNase. On the basis of spectral data, gel permeation chromatography, affinity adsorption and electron microscopic visualization, the poly(G) x poly(C) product was assumed to possess a high degree of structural regularity. Its in vitro and in vivo antiviral activities were compared with those of traditional poly(G) x poly(C) and poly(I) x poly(C). Template-dependent poly(G) x poly(C) was similar in its in vitro activity to poly(I) x poly(C) or even surpassed it, whereas the 'traditional' poly(G) x poly(C) was only slightly active in vitro. However, 'traditional' poly(G) x poly(C) and poly(I) x poly(C) had similar activity in vivo, whereas template-dependent poly(G) x poly(C) was much less active in vivo. The role of intramolecular structural regularity in the in vitro and in vivo antiviral activity of polyribonucleotide duplexes is discussed.

Animals↗

PubMed1985

Comparison between poly(dG-dC).poly(dG-dC) and DNA modified by cis-diamminedichloroplatinum (II): immunological and spectroscopic studies.

The importance of the base composition and of the conformation of nucleic acids in the reaction with the drug cis-diamminedichloroplatinum(II) has been studied by competition experiments between the drug and several double-stranded polydeoxyribonucleotides. Binding to poly(dG).poly(dC) is larger than to poly (dG-dC).poly(dG-dC). There is no preferential binding in the competition between poly(dG-dC).poly(dG-dC), poly(dA-dC).poly(dG-dT) and poly(dA-dG).poly(dC-dT). In the competition between poly(dG-dC).poly (dG-dC) (B conformation) and poly(dG-br5dC).poly(dG-br5dC) (Z conformation), the drug binds equally well to both polynucleotides. In natural DNA, modification of guanine residues in (GC)n.(GC)n sequences by the drug has been revealed by the inhibition of cleavage of these sequences by the restriction enzyme BssHII. By means of antibodies to platinated poly(dG-dC), it is shown that some of the adducts formed in platinated poly(dG-dC) are also formed in platinated pBR322 DNA. The type of adducts recognized the antibodies is not known. Thin layer chromatography of the products after chemical and enzymatic hydrolysis of platinated poly(dG-dC) suggests that interstrand cross-links are formed. Finally, the conformations of poly(dG-dC) modified either by cis-diamminedichloroplatinum(II) or by trans-diamminedichloroplatinum (II) have been compared by circular dichroism. Both the cis-isomer and the trans-isomer stabilize the Z conformation when they bind to poly(dG-m5dC) in the Z conformation. When they bind to poly(dG-m5dC) in the B conformation, the conformations of poly(dG-m5dC) modified by the cis or the trans-isomer are different. Moreover, the cis-isomer facilitates the B form-Z form transition of the unplatinated regions while the trans-isomer makes it more difficult.

Binding, Competitive↗