Fractions Of Poly Research Articles

The lognormal distribution fits the decay profile of eukaryotic mRNA

A general program was written which simulates radioactive labeling of RNA in vivo . The program was used to determine the effect that different distributions of half-lives would have on the composite decay curve observed in a pulse-chase experiment. Four biologically relevant points emerge: 1) The published, experimentally determined composite decay curves for eukaryotic mRNA are not compatible with a normal, uniform, or exponential distribution of decay times. 2) The experimental curves are compatible with a lognormal distribution of decay times as well as the two-component discrete distribution previously hypothesized. 3) If the lognormal or some similar distribution were correct, about half the mRNA species would decay faster than what is presently called the “fast component of decay”. This point is crucial to any argument about the fraction of poly (A) or other nuclear sequence that is transported to the cytoplasm. 4) If a particular mRNA species is found to decay at a constant rate for 3 half-lives, that is not only consistent with 1 half-life for all the mRNA, but also consistent with 20 different half-lives which are normally or uniformly distributed. In addition to the decay of mRNA, the lognormal distribution is also compatible with data on the decay of poly(A)-containing nuclear RNA and total cellular protein.

Fractionation and characterization of rat liver poly(A)-containing RNA

Three fractions of poly(A)-containing RNA were separated from total rat liver RNA using poly(U)-Sepharose 4B affinity chromatography. The poly(A)-containing RNA fractions were released by thermal elution. Fraction 1, eluted under the mildest conditions, and had poly(A) tracts of approx. 200 AMP units in length which appeared to be associated with poly(U) sequences of 20–50 UMP in length. Fraction 1 appeared to be present mainly in the nucleus and, its size distribution was similar to that of fractions 2 and 3. Fractions 2 and 3 eluted at higher temperatures and were associated mainly with polysomal and microsomal fractions. Poly(U) sequences were absent in fractions 2 and 3 while their poly(A) sequences had a size distribution characteristic of those reported in the mRNA of other organisms.

A simple method for electrophoretic selection and fractionation of poly(A)-containing RNA and poly(A)

A simple procedure, useful for quantitative and qualitative assays of poly(A)-containing RNA and poly(A), as well as for preparative purposes, is described. Glass-fiber filters with immobilized poly(U), a well-known technique for absorption of poly(A)-containing RNA, is combined with electrophoresis in a gel slab of agarose. In front of each of the two troughs in a gel slab, glass-fiber filters are inserted, one of which is impregnated with poly(U). Two identical RNA samples, e.g., split samples of total RNA from salivary glands of Chironomus tentans, are applied to the troughs and are moved electrophoretically across two different filters. The electrophoresis is conducted under conditions which promote the formation of duplexes between absorbed poly(U) and moving poly(A). While the passage of RNA chains across the control filter may take place essentially freely, RNA molecules that contain poly(A) hybridize with poly(U) fixed in the glass-fiber filter and become trapped there. The difference between resulting gel profiles [pattern of the total RNA minus the pattern of RNA not containing poly(A)] yields the electrophoretic distribution of poly(A)-containing RNA. In addition, poly(A)-containing RNA can be eluted from the poly(U) filter with formamide and subjected to electrophoresis without a subsequent precipitation in ethanol. No measurable quantities of ribosomal RNA or tRNA are retained on the poly(U) glass-fiber filters. The hybridization technique enables a quantitative retention of poly(A) molecules representing a wide range of chain lengths.

13C n.m.r. study of optically active polymers: 2. Relaxations in poly [(S)-4-methyl-1-hexene

T 1, T 2 and NOE were measured in 13C n.m.r. spectra of two fractions of poly [(S)-4-methyl-1-hexene] obtained by selective solvent extraction (diethyl ether and cyclohexane) of the polymers prepared in the presence of isospecific catalysts. T 1 measurements provide evidence in the two fractions for the existence of different conformational weightings about side chain bonds according to conclusions from vibrational spectroscopy studies. Subtle configurational differences of the two substantially isotactic samples are suggested to explain this result. A discussion of the dynamic parameters related to the correlation time is also presented which supports the above explanation.

The Mechanism of Codon-Anticodon Interaction in Ribosomes. Quantitative Study of Codon-Dependent Binding of tRNA to the 30-S Ribosomal Subunits of Escherichia coli

The formation of a ternary complex 30-S-subunit . poly(U) . tRNAPhe is discussed and the conditions for its correct description by Langmuir's isotherm are deduced. The affinity constant of the binary complex 30-S-subunit . poly(U) is measured. The reversibility of binding of tRNAPhe to the complex 30-S-subunit . poly(U) is proved in a direct way. The main reason for the heterogeneity of ternary complexes was found to be due to the ability of high-molecular-weight poly(U) to form complicated aggregates with 30-S subunits. If a fraction of poly(U) of moderate molecular weight (30 000) is used, then the ternary complexes are homogeneous in stability and yield the same affinity constants for deacylated, aminoacylated and peptidyl-tRNAPhe (1 X 10(8) M-1 at 20 mM Mg2+, 200 mM NH+4 and 0 degrees C). Ribosomal protein S1 increases the binding constant of poly(U) with 30-S subunits but does not change the binding constant of tRNAPhe with the 30-S-subunit . poly(U) complex. All 30-S subunits, even partially stripped of S1 protein, are active in the binding of both poly(U) and tRNAPhe.

Messenger RNA for G1 protein of French bean seeds: Cell-free translation and product characterization

The fraction of poly(A)-containing RNA isolated from ripening bean (Phaseolus vulgaris) cotyledons that sedimented at 16 S in linear logarithmic sucrose gradients was at least as active a messenger as viral RNA when added to a cell-free protein-synthesizing system from wheat germ. The major products synthesized in vitro were polypeptides of about 47,000 and 43,000 daltons, corresponding to two of the three subunits of G1 protein, the most abundant bean seed storage protein. No trace of the largest (53,000 daltons) subunit was found among the polypeptides synthesized in vitro. Proof that the 47,000- and 43,000-dalton polypeptides coded by the 16S RNA were indeed subunits of G1 protein was obtained by immunoprecipitation with monovalent antibody to G1 protein and by electrophoretic mapping of peptides on acrylamide gels after digestion of mixtures of authentic protein and radioactive translation products with protease V8, chymotrypsin, and trypsin. The subunits synthesized in vitro were slightly smaller than the native subunits, probably because they lacked the sugar residues present on the holoprotein.

Temperature dependence of morphology of supermolecular structures growing in the thin layer melt of fractions of poly(ethylene oxide)

Abstract Poly(ethylene oxide) fractions with molecular weights in the range from 1.55 × 103 to 1.5 × 105 were studied. The optical microscopic observations of the morphology of supermolecular structures grown isothermally from the melt were used to determine the dependance of structural-morphological changes on temperature. Two morphological transitions were established: (1) a high temperature transition at 49 [Ptilde] 3° C from hedritic structures to positive spherulitoids and (2) a low temperature transition at 38 [Ptilde] 2° C from positive spherulitoids to negative spherulites. It is supposed that the transition from hedrites to positive spherulitoids proceeds through a transition from b-axis-oriented lamellae with tilted chains to [401] lamellae with chains perpendicular to the lamellar surface.

Fractionation of Poly(vinyl chloride)s by Preparative Scale Gel-Permeation Chromatography

Three poly(vinyl chloride) (PVC) samples were fractionated by a preparative-scale GPC (gel-permeation chromatography) with Styragel. The carrier solvent used was tetrahydrofran. The fractionation of one sample whose average molecular weight was the lowest among the three samples was not affected much by the injected sample concentration and all the fractions obtained gave fairly narrow distributions of molecular weight. The fractionation of the remaining two samples having higher average molecular weights showed an overload effect and the polydispersity of each fraction of these samples was greater than that of the former sample. The relationship between the intrinsic viscosity and weight-average molecular weight for PVC fractions revealed that the fractions of the latter two samples contained long chain branches. The GPC calibration curve for the hydrodynamic volume of PVC agreed with that of the polystyrene standards in the low molecular-weight range, but not in the high molecular-weight range where the effect of chain branching was dominant.

Influence of stereoregularity on precipitation fractionation of poly(vinyl chloride) in THF-H2O

Abstract Anomalies during precipitation fractionation of PVC from THF solution with H20 as nonsolvent were investigated by using GPC and solution infrared techniques. The data indicate that separation during the fractionation takes place by both stereoregularity and molecular weight because of the formation of molecular aggregates during the precipitation and collection of fractions. The separation by stereoregularity dominates at the beginning of the fractionation. The aggregates formed at this point are comprised of highly syndiotactic molecular segments which tend to precipitate before segments of lower stereo-regularity but higher molecular weight. For the first few fractions, molecular weights recorded may be seriously overestimated unless care is taken to disperse the aggregates by appropriate heating of the solutions used for GPC characterizations. After 25-30% of the polymer precipitates, the fractionation becomes independent of stereoregularity and proceeds according to molecular weight. While th...

Dimensions of poly(trimethylene oxide) chains in a theta-solvent

Fractions of poly(trimethylene oxide) CH 2) 3] x of relatively high degree of polymerization x were studied in liquid-liquid phase equilibria in the poor solvent cyclohexane. The results thus obtained indicate that the ideal or theta-temperature for this system is 27.0 ± 0.5°C. Intrinsic viscosities measured under these conditions were used to obtain a value for the characteristic ratio 〈r 2〉 0 nl 2 of the unperturbed dimensions of these chains relative to the number of skeletal bonds and the average square of their length. The resulting value, 3.86 ± 0.08, is unusually low, a fact which may be attributed to the high degree of conformational randomness in this chain molecule. Consideration of poly(trimethylene oxide) to be an alternating copolymer of ethylene and oxymethylene provides some additional information of interest. It clearly demonstrates that a chemical copolymer can have configuration-dependent properties which are vastly different from those of its parent homopolymers.

RNA synthesis in cells infected with herpes simplex virus. XII. Sequence complexity and properties of RNA differing in extent of adenylation

Fractionation of polyadenylated RNA from cells infected with herpes simplex virus by affinity chromatography on columns of poly (U) immobilized on glass-fiber filters yielded three major classes of RNA-containing poly(A) chains with average lengths of 30, 50, and 155 adenylate residues [poly(A)30, poly(A)50, poly(A)155]. In contrast, nitrocellulose membranes bound predominantly a fraction of RNA containing poly(A)155. The distribution of cytoplasmic RNA in the three classes was found to be independent of the labeling interval, ranging from 10 min to 6 h. Cytoplasmic poly(A) RNA consisted mainly (57 to 68%) of the poly(A)155 class; this was also the major class (68%) of polyadenylated RNA found in polyribosomes. Nuclear poly(A) RNA consisted largely (42 to 50%) of poly(A)30 class, whereas high-molecular-weight nuclear RNA sedimenting at greater than 45S contained almost exclusively the poly(A)30 tracts. Hybridization experiments involving unlabeled RNA and labeled viral DNA demonstrated the presence of viral RNA sequences complementary to approximately 40% of viral DNA in all polyadenylated RNA classes. Inasmuch as unfractionated cytoplasmic RNA arises from approximately 40% of the viral DNA, we conclude that most, if not all, viral RNA species present in the cytoplasm are adenylated. In contrast to these results, only a fraction of poly(A)155 RNA, complementary to 21% of viral DNA, bound to nitrocellulose filters. The selective binding of poly(A)155 sequences to nitrocellulose filters might be related to its secondary structure, since transcripts homologous to 40% of viral DNA bind to nitrocellulose membranes, provided the RNA is denatured prior to filtration. The data suggest that poly(A) tracts arise by at least two separate steps. The first involves the appearance of poly(A)30 tracts in the high-molecular-weight nuclear transcripts. The second involves polyadenylation to ply(A)50 and poly(A)155 RNA classes concomitant with processing and transport to the cytoplasm.

Crystallization of poly(ethylene oxide) fractions: simultaneous dilatometry and calorimetry

The crystallization of two fractions of poly(ethylene oxide), with molecular weights of 6000 and 360 000, has been studied by simultaneous dilatometry and calorimetry. The crystallization isotherms obtained by the two techniques are identical for the low molecular weight fraction, but differ for the high molecular weight fraction.

Poly[N-(2-hydroxypropyl)methacrylamide]—II: Hydrodynamic properties of dilute solutions

The results of viscosity and light scattering measurements on fractions of poly[N-(2-hydroxypropyl)methacrylamide] in several solvents were used for the determination of the parameters of the Mark-Houwink equation, characteristic ratio and its temperature coefficient and the parameters of the polymer-solvent interaction. The solutions in water and in aq. NaCl are exothermal, in dimethylformamide approx. athermal, and in ethanol endothermal. The effect of the solvent on the short-range interactions between the polymer chain units was also demonstrated.

Fractionation of Poly(γ-b-enzyl-L-glutamate) by Gel-Permeation Chromatography

Gel-permeation chromatography (GPC) was utilized for fractionating poly(γ-benzyl-L-glutamate) (PBLG) polymerized from N-carboxylanhydrides. The resolving power of this GPC column was checked by several monodisperse materials such as Gramicidin D, carbobenzoxy-L-Leu-L-Leu-L-Val-L-Phe-methyl ester, diketopiperazine, and 1,2,4-trichlorobenzene (TCB). The fractionation efficiency was analyzed by comparison of the molecular-weight distribution of fractionated PBLG and that of unfractionated PBLG, which was determined by the relation between molecular weights of PBLG samples and their elution volumes. On the basis of these results we conclude that GPC offers a useful method of obtaining the monodisperse PBLG whose Mw/Mn ratio is less than 1.1.

Solution properties of polysulphones of some 1,2-disubstituted alkenes

Fractions of poly(cyclohexene sulphone), M ̄ n = 22 500–324 000 , and poly(cyclopentene sulphone), M ̄ n = 47 200–571 000 , were prepared. Unlike poly(hex-1-ene sulphone) and poly(2-methylpent-1-ene sulphone), neither of these polymers, nor poly(but-2-ene sulphone) nor poly(hex-2-ene sulphone), showed any dielectric dispersion in solution over the frequency range 2 × 10 2 to 1.2 × 10 7Hz. The dielectric increment was similar in magnitude to the high frequency value for poly(hex-1-ene sulphone) and poly(2-methylpent-1-ene sulphone), and was attributed entirely to distortion polarization. The absence of a permanent dipole indicates that in the polysulphones of 1,2-disubstituted alkenes the CC bonds are all in the trans conformation, whether or not the alkene has a cyclic structure. Unperturbed dimensions were calculated from viscosity data and compared with those calculated for free rotation about the two CS bonds in each repeat unit, the CC bonds being assumed to be all in the trans conformation. The observed values are not greatly in excess of the free-rotation values.

Effect of molecular weight on the crystallization and morphology of poly (ethylene oxide) fractions

AbstractThe temperature dependence of the isothermal growth rate of spherulites and overall crystallization kinetics of different fractions of poly (ethylene oxide) over the range of molecular weight from 300 to 20,000 were studied by calorimetry, dilatometry, and polarized light microscopy, in order to establish the dependence of the kinetic parameters upon molecular weight. The morphology of crystallites was studied by small‐angle x‐ray scattering. In the course of this study it has been established that the growth rates of spherulites and the overall crystallization rates at any fixed supercooling essentially depend upon molecular weight. The minimum in the crystallization rate which occurs at molecular weight 4000 is a consequence of transition from extended‐chain crystallization to folded‐chain crystallization. Small‐angle x‐ray scattering study of the morphological features confirmed this conclusion. This minimum depends very strongly on the degree of supercooling, increasing rather sharply at small supercooling. The temperature and molecular weight dependence of the growth rates of spherulites and the overall crystallization rates has been analyzed by means of the theoretical expression given by Hoffman and Lauritzen. The product of the lateral and basal surface free energies of the crystallites σσe increases with molecular weight and reaches a limiting value at molecular weight 6000. Such behavior is in agreement with morphological transformations.

Fractionation of poly(vinyl alcohol) derived from poly(vinyl acetate) from its aqueous solution induced by shearing force-IV

In order to clarify the mechanism of crystallization under molecular orientation, the fractionation for poly(vinyl alcohol) (VAc-PVA) derived from vinyl acetate from its aqueous solution was carried out under shearing force. The fibrillar crystals grown by shearing force from solutions were produced on the stirrer and in solution simultaneously. The fibrillar crystals had a diameter of approximately 1 mm and a length of 1 cm in the case of the initial polymer concentration of 2.0%, and approximately 1 mm and 5 cm in the case of 0.5%. The initial rate of precipitation (Rs) for the precipitates produced in solution was higher than that (Rr) on the stirrer. The difference betweenRs andRr increased with an increase in initial polymer concentration. The difference in the percentages of syndiotactic diads of precipitates grown on the stirrer and those in solution was not found, and the percentages of syndiotactic diads of each fraction decreased in the order of fractionation. Furthermore, the difference in the molecular weight of precipitates grown on the stirrer and those in solution was not found in the case of the higher polymer concentration, whereas it was found clearly in the case of lower one.

Properties of ethylene–propylene–vinyl chloride graft copolymers. II. Viscoelasticity and composition of graft copolymer and composite

AbstractThe viscoelasticity and volume expansion of the raw polymerizate of ethylene–propylene copolymer with vinyl chloride grafts, and of the individual components has been studied. The raw polymerizate (composite) and the pure ethylene–propylene–vinyl chloride graft copolymer were found to consist of two phases. The pure graft copolymer has an ethylene–propylene matrix containing some fraction of poly(vinyl chloride) (PVC) grafts and a microphase with the remainder of the PVC grafts. The raw polymerizate consists of a PVC matrix plasticized with ethylene–propylene chains and a microphase of the ethylene–propylene copolymer. An attempt has been made to calculate the participation of components in microphases and the minimum dimension of the PVC microphase aggregates.

Fractionation of poly (dA-dT) by gel chromatography.

AbstractA commercial sample of poly (dA‐dT), a copolymer of 2′‐deoxyribosyladenosine (dA) and 2′‐deoxyribosylthymidine (dT) of perfectly alternating sequence, was fractionated by chromatography on Agarose gel. Paucidisperse fractions of different molecular size were obtained. The plot of log s020,w values shows a linear dependence on Ve. The buoyant densities of individual fractions do not differ over the molecular size range studied. On the other hand, the heat‐induced hyperchromic effect was found to depend on molecular size below a certain limit, s020,w = 4.12 S.

Fractionation of poly(methyl methacrylate) by precipitation chromatography

Three radically initiated poly(methyl methacrylate) samples have been prepared and fractionated by precipitation chromatography. Fractions in the mol. wt. range 0·37–34·6 × 10 5 have been isolated. Successful resolution of high mol. wt. poly(methyl methacrylate) was accomplished with a narrow temperature gradient, a slow elution flow rate, a slow change in solvent—non-solvent composition, and a high ratio of mixing vessel to polymer load. The fractions were examined by turbidimetric titration and were refractionated by precipitation chromatography and gel permeation chromatography. The fractions were found to have narrow symmetrical mol. wt. distributions, confirming the efficiency of precipitation chromatography and the use of the Schulz—Dinglinger procedure for the treatment of fractionation data. It is suggested that, for high mol. wt. poly(methyl methacrylate), fractionation by solubility may be influenced by polymer adsorption onto the column packing.