Basis Of Poly Research Articles

Interaction of aromatic residues of proteins with nucleic acids. Circular dichroism studies of the binding of oligopeptides to poly(adenylic acid)

The binding of peptides containing lysyl and aromatic residues to poly(A) in its single-stranded form at pH 7 leads to a change of its circular dichroism (CD) spectrum, which is mainly due to the stacking of the aromatic amino acid with the bases of poly(A). Comparison is made between the binding of peptides having different primary structures which gives indications on the way the peptides bind to poly(A). A method is described which allows the calculation of the binding parameters from CD data. The magnitude of the association constant depends on the size of the aromatic ring and decreases in the order tryptophan greater than tyrosine greater than phenylalanine. The CD amplitude decreases linearly with the concentration of bound molecules. These results are discussed with respect to the role played by aromatic amino acids in complex formation between nucleic acids and proteins.

Two classes of cytoplasmic viral RNA synthesized early in productive infection with adenovirus 2.

The RNA sequences and RNA size classes transcribed early in productive infection with adenovirus 2 were analyzed by RNA-DNA hybridization. Two independent procedures demonstrated that early cytoplasmic viral RNA is composed of two sequence classes, class I which is absent or present in greatly reduced quantities at 18 h, and class II which persists throughout the infection. When the sequences in early viral RNA were analyzed by hybridization-inhibition studies, the hybridization of early [(3)H]RNA was inhibited only 50% by RNA from cultures harvested late (18 h) in infection. Liquid hybridizations with radioactive viral DNA confirmed that early RNA includes two classes. Duplex formation of RNA with (32)P-labeled viral DNA was assayed by hydroxylapatite chromatography and resistance to S(1) nuclease digestion. Both methods showed that the cytoplasmic RNA present early in infection annealed 12 to 15% of the viral DNA; late cytoplasmic RNA hybridized 21 to 25% of the DNA. Mixtures of early plus late cytoplasmic RNAs hybridized 30 to 34% of the viral DNA, demonstrating the reduced concentration of early class I RNA in the late RNA preparations. Experiments were performed to correlate class I and class II early RNA with size-fractionated cytoplasmic RNA synthesized early in infection. Fractionation of RNA by gel electrophoresis or sucrose gradient centrifugation confirmed three major size classes, 12 to 15S, 19 to 20S, and 26S. Total cytoplasmic RNA and RNA selected on the basis of poly(A) content contained the same size classes of viral RNA. In standard electrophoresis conditions, the 19 to 20S viral RNA could be resolved into two size classes, and the distribution of 12 to 15S RNA also indicated the presence of more than one size component. Hybridization-inhibition studies under nonsaturating conditions were performed with 26S, 19 to 20S, and 12 to 15S viral RNAs fractionated by gel electrophoresis. Late RNA inhibited the hybridization of 26S RNA only 20%, 19 to 20S RNA was inhibited 45%, and 12 to 15S RNA was inhibited 50%. When 18 to 19S and 12 to 15S viral RNAs purified by sucrose gradient centrifugation were similarly analyzed, late RNA inhibited hybridization of 18 to 19S RNA 50%, and the annealing of 12 to 15S RNA was inhibited 70%.

The interactions of 2-thiopyrimidine bases with hydroxymercurybenzene sulfonate.

The interaction of hydroxymercurybenzene sulfonate (HOHgBzS) with 2‐thiouridine (s2Urd) and 2‐thiocytidine (s2Cyd) by means of absorption‐difference spectroscopy and spectrophotometric titration was investigated. The absorption spectra of the reaction mixtures displayed isosbestic points indicating uniform reactions. Scatchard plots of the titration data revealed the formation of 1:1 complexes with a dissociation constant for s2Urd · HOHgBzS and s2Cyd · HOHgBzS of Kd= 0.55 μM and Kd= 0.54 μM, respectively. The interactions of poly(s2U) and poly(s2c) with hydroxymercurybenzene sulfonate were established by their corresponding absorption difference spectra. The binding of hydroxymercurybenzoate (HOHgBz) to poly(s2C) and poly(s2U) was investigated by means of equilibrium dialysis. The association of HOHgBz to 2‐thiocytosine bases in poly(s2C) follows a simple hyperbolic binding isotherm. The Scatchard plot of the binding data disclosed that only a fraction (n= 0.32) of the s2CMP residues in poly(s2C) was accessible to the interaction with HOHgBz. The dissociation constant of this interaction was found to be Kd= 4.3 μM. The binding of HOHgBz to the helical poly(s2U) is a cooperative process as indicated by the sigmoidal binding cuve. Under saturating conditions all s2UMP residues in poly(s2U) interact with the ligand.

Oxidation of ribonucleic acids with m-chloroperbenzoic acid.

Reaction conditions are described under which treatment with m-chioroperbenzoic acid yields N-oxides of poly-(adenylic acid) and poly(cytidylic acid), but not of poly(uridylicacid), poly(guanylic acid), orpoly(inosinicacid). The interaction of poly(A)N-oxides with poly(U) and poly(C)N-oxides with poly(I) decreases with increasing degree of oxidation. The rates of oxidation of adenine and cytosine bases in poly(A)˙poly(U) and poly(I)·poly(C) are less than the rates of oxidation of the same bases in poly(A) and poly(C), but oxidation does not occur selectively in single-stranded regions, as reported previously for oxidation with monoperoxyphthalic acid. Oxidation of a natural double-stranded RNA occurs at adenine, cytosine, and guanine units.

Oligomeric initiators of radical polymerization on the basis of poly(phenylene toluylene esters)

By the oxidation of some alkylene aromatic oligomers under soft conditions we succeeded in introducing into them peroxide-type groups containing active oxygen. Such oligomers may be used as explosion-proof initiators of radical polymerization of vinyl monomers. In addition to initiation, similar oligomers can act as agents, modifying the properties of the polymers obtained. Oxidation in different solvents of poly (phenylene toluylene ethers) (PPTE), obtained by condensation of difterent substitutes of diphenyl ether of general formula X-CH2 , where X = Cl, OH, OCH3, OC2H5, and Y = H or CH2 X, allows the introduction 0.2–0.5% of active oxygen into them. Stability of peroxide groups in oxidized PPTE has been estimated under various conditions. The initiating activity of oxidized PPTE in polymerization of styrene at 80° is arranged in succession depending on the nature of the X substitute: OCH3 > OC2H5 > Cl.

An analysis of the results for the binding of formaldehyde to polyuridylic acid.

AbstractSpectrophotometric measurements were made on the extent of binding of formaldehyde to polyuridylic acid under conditions of varying temperature and formaldehyde concentration. The data is interpreted in terms of a temperature‐dependent stacking of the bases in poly U at 20°, but not at 40°C. A theory of cooperative stacking is developed which considers the base residues to be either non‐bonded, non‐bonded and methylolated, or stacked. The results indicate essentially non‐cooperative base stacking under these conditions with an equilibrium constant for base stacking of 0.92 at 20°C.

Tolerance of modified poly(glycol methacrylates) by the organism.

AbstractInvestigation has been made of the short‐term tolerance of hydrophilic polymers on the basis of poly(hydroxy ethyl methacrylates) containing various amounts of acidic and basic groups. The worst tolerance was found with gels containing basic groups alone.

NMR study of poly(vinyl formate)

AbstractThe high resolution nuclear magnetic resonance spectrum of poly(vinyl formate), yielded, upon examination at 100 Mc./sec., and under the conditions of decoupling, information on the three tactic forms present. The normal and decoupled spectra indicate that only the CHO resonance is sensitive to the stereochemical configuration. The three components of the CHO resonance are tentatively assigned to isotactic (i), heterotactic (h), and syndiotactic (s) triads with increasing field strength, respectively. This assignment was made on the basis of poly(vinyl alcohol) and poly(vinyl acetate) derived from poly(vinyl formate). The results show that the tacticity is slightly dependent upon the temperature of free‐radical polymerization.