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At least 109 records · Page 6Linked to original sources
PubMed1976

Newcastle disease virus-specific RNA: poly(A)-containing and poly(A)-deficient transcripts as revealed by chromatography on poly(U)-sepharose.

Total [3H]uridine-labeled, virus-specific RNA from Newcastle disease virus-infected cells was fractionated by poly(U)-sepharose chromatography and analyzed by rate zonal gradient centrifugation. The sedimentation pattern of both eluted and nonadsorbed RNA resembled that of the total RNA. However, nonadsorbed RNA was enriched in 50S material, ant its 18S peak was broader and slightly shifted towards the top of the gradient. Poly(U-sepharose chromatography of isolated 18S RNA and 24S RNA resulted in the separation of poly(A)-containing RNA and poly(A)-deficient RNA. In the former the percentage of adenosine content represented by poly(A) sequences was estimated as 10 to 12% (for 18S RNA) or approximately 6.0% (for 24S RNA). The size of poly(A) fragments as measured by their sedimentation rate was the same for 18S and 24S RNA. Polyacrylamide gel electrophoresis of poly(A)-containing RNA revealed a characteristic pattern closely resembling the pattern of nonchromatographed 18S and 24S RNA. The pattern of poly(A)-deficient RNA was heterogenous, and for 18S RNA it shifted towards the anode. The possible origin of poly(A)-deficient transcripts is discussed.

Base Sequence↗
PubMed1986

Poly(ADP-ribose) accessibility to poly(ADP-ribose) glycohydrolase activity on poly(ADP-ribosyl)ated nucleosomal proteins.

Hydrolysis of protein-bound 32P-labelled poly(ADP-ribose) by poly(ADP-ribose) glycohydrolase shows that there is differential accessibility of poly(ADP-ribosyl)ated proteins in chromatin to poly(ADP-ribose) glycohydrolase. The rapid hydrolysis of hyper(ADP-ribosyl)ated forms of histone H1 indicates the absence of an H1 dimer complex of histone molecules. When the pattern of hydrolysis of poly(ADP-ribosyl)ated histones was analyzed it was found that poly(ADP-ribose) attached to histone H2B is more resistant than the polymer attached to histone H1 or H2A or protein A24. Polymer hydrolysis of the acceptors, which had been labelled at high substrate concentrations (greater than or equal to 10 microM), indicate that the only high molecular weight acceptor protein is poly(ADP-ribose) polymerase and that little processing of the enzyme occurs. Finally, electron microscopic evidence shows that hyper(ADP-ribosyl)ated poly(ADP-ribose) polymerase, which is dissociated from its DNA-enzyme complex, binds again to DNA after poly(ADP-ribose) glycohydrolase action.

Animals↗
PubMedDate not supplied

[Influence of a complex of poly(I). poly(C) and poly-l-lysine on the course of vaccinia in monkeys].

Experiments of 22 Macaca rhesus monkeys were carried out to study the interferon-inducing and antiviral activity of poly(I) - poly(C) and of its complex with poly-l-lysine. The complexed double-stranded polyribonucleotide induced active production of serum interferon and markedly protected the monkeys inoculated intradermally with vaccinia virus (10 monkey ID50 by intradermal inoculation). The effectiveness of the protective effect depended on the schedule and routes of administration of the preparation. The greatest prophylactic and therapeutic effect was achieved by local administration of the complex in a dose of 1 mg/1 kg of body weight. This also prolonged the incubation period by 2-3 times and reduced the duration of persistence of skin lesions approximately by half. By the intravenous route, the best protection was achieved by 2 injections of 2 mg/kg at an interval of 96 hours. Four daily injections of the complex exerted virtually no effect on the course of vaccinia infection. The animals receiving the complexed poly(I) - poly(C) developed virus-neutralizing antibody to the same titres as control animals and were resistant to reinfection with vaccinia virus. A second injection of the complexed poly(I)-poly(C) 96 hours after the primary inoculation induced the same interferon production as the initial administration of the preparation. The monkeys inoculated intravenously with 2 mg/kg poly(I) - poly(C) showed no interferon in their blood serum and were also poorly protected against vaccinia virus infection.

Animals↗
PubMed1988

Proton magnetic resonance studies of the binding of oligopeptides containing tryptophan to polyribonucleotides poly A, poly U and poly C.

The binding of oligopeptides Lys-Trp-Gly-Lys OtBu, Lys-Gly-Trp-Lys OtBu and Lys-Trp-Lys to Polyadenylic, Polycytidylic and Polyuridylic acid has been studied by Proton NMR at 90 MHz and 500 MHz at oligopeptide/Polynucleotide ratios ranging from 0.01 to 0.20 at 275-365 K. Downfield shift of 0.01-0.2 ppm at 296 K of the H2, H8 and H1' resonances of Poly A due to binding with oligopeptides is accompanied by a marked narrowing of resonance lines of Poly A. The ring protons of tryptophan shift upfield by 0.3-0.6 ppm at 296 K on binding to Poly A. Changes in chemical shift of both adenine and tryptophan protons on binding are much smaller at 355 K than that at 275 K. These observations are ascribed to intercalation of the tryptophan ring in the adenine bases resulting in partial destacking of adenine bases in Poly A. Using the magnetic anisotropy ring current shifts, an overlap geometry of tryptophan ring in the adenine has been proposed. Addition of oligopeptides to Poly C and Poly U, on the other hand, suggests that tryptophan ring does not stack in Poly U and Poly C.

Magnetic Resonance Spectroscopy↗
PubMed1998

Poly(A)-driven and poly(A)-assisted termination: two different modes of poly(A)-dependent transcription termination.

We mapped the elements that mediate termination of transcription downstream of the chicken betaH- and betaA-globin gene poly(A) sites. We found no unique element and no segment of 3'-flanking DNA to be significantly more effective than any other. When we replaced the native 3'-flanking DNA with bacterial DNA, it too supported transcription termination. Termination in the bacterial DNA depended on a functional poly(A) signal, which apparently compelled termination to occur in the downstream DNA with little regard for its sequence. We also studied premature termination by poorly processive polymerases close to the promoter. The rate of premature termination varied for different DNA sequences. However, the efficiencies of poly(A)-driven termination and promoter-proximal premature termination varied similarly on different DNAs, suggesting that poly(A)-driven termination functions by returning the transcription complex to a form which resembles a prior state of low processivity. The poly(A)-driven termination described here differs dramatically from the poly(A)-assisted termination previously described for the simian virus 40 (SV40) early transcription unit. In the SV40 early transcription unit, essentially no termination occurs downstream of the poly(A) site unless a special termination element is present. The difference between the betaH-globin and SV40 modes of termination is governed by sequences in the upstream DNA. For maximum efficiency, the betaH-globin poly(A) signal required the assistance of upstream enhancing sequences. Moreover, the SV40 early poly(A) signal also drove termination in betaH-globin style when it was placed in a betaH-globin sequence context. These studies were facilitated by a rapid, improved method of run-on transcription analysis, based on the use of a vector containing two G-free cassettes.

Animals↗
PubMed2005

Microwave-assisted synthesis of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) tri-block co-polymers and use as matrices for sustained delivery of ibuprofen taken as model drug.

Poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) triblock co-polymers with number-average molar mass (Mn) over 20000 g/mol were prepared by ring-opening polymerization of epsilon-caprolactone initiated by poly(ethylene glycol) under microwave irradiation. This method was proposed as a means to improve in vivo compatibility as no harmful chemicals were involved in the polymerization except epsilon-caprolactone and poly(ethylene glycol). The resulting tri-block co-polymers were characterized by FT-IR, H-NMR, GPC and WAXD. Their Mn and their composition was controlled by the amount and the chain length of the poly(ethylene glycol) macromers involved in the feed. The ability of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) co-polymers to entrap and deliver drugs was investigated with ibuprofen as a model drug. The release of ibuprofen was significantly influenced by the co-polymer composition and the extent of loading. The in vitro release of ibuprofen was sustained from 3 to 15 days for 10% loading, depending on the ratio of epsilon-caprolactone to ethylene glycol-derived subunits in co-polymer chains. This ratio ranged from 0.97 to 9.78. In the case of the co-polymer whose epsilon-caprolactone molar ratio to ethylene glycol-derived subunits was 2.49, the ibuprofen release was sustained for 2 to 24 days for ibuprofen loads going from 5 to 20 wt%.

Drug Delivery Systems↗
PubMed1976

Analysis of the role of different cell types in the genetic regulation of antibody production to the thymus-independent synthetic polypeptide poly (DTyr, DGlu)-poly (DPro)--poly (DLys).

The immune response potential of mice to the thymus-independent synthetic polypeptide poly (DTyr, DGlu)-poly(DPro)--poly(DLys)[D(T,G)-Pro--L] is genetically regulated. The defect in the ability of low responder mice to mount an immune response to this antigen appears to be expressed in their B cell population since the presence of thymocytes, or addition of "educated T cells" or supernatant of T cells after stimulation with the antigen neither enhanced, nor suppressed the level of antibodies produced in both low and high responder mice. Low responsiveness could not be enhanced either by stimulation of macrophages or by injection of poly(A) - poly(U) in contrast to the significant effect of these agents on low responses to the thymus-dependent poly(LTyr, LGlu)-poly(LPro)--poly(LLys) [L(T,G)-Pro--L]. These results suggest that macrophages do not participate in the limiting step, or are not involved at all, in antibody production towards the thymus-independent polypeptide. The antibodies produced in response to D(T,G)-Pro--L were found to be mainly of the 7 S class. T cells are not required for the production of mercaptoethanol resistant antibodies to this immunogen since they were found in intact mice as well as in T cell depleted animals.

Animals↗
PubMed1986

Interaction of transition metal ions with Z form poly d(A-C).poly d(G-T) and poly d(A-T) studied by I.R. spectroscopy.

Interactions between Ni2+, Co2+ and purine bases have been studied by I.R. spectroscopy in the case of double stranded regularly alternating purine-pyrimidine polynucleotides poly d(A-T), poly d(A-C).poly d(G-T) and poly d(G-C). The spectra of polynucleotide films have been recorded in hydration and salt content conditions which correspond to the obtention of the classical right-handed (A,B) and left-handed (Z) helical conformations. Selective deuteration of the 8C site of purines has been obtained and is used to detect interactions between the transition metal ions and the adenine or guanine bases. The spectral region between 1500 and 1250 cm-1 corresponding to base in-plane vibrations and involving also the glycosidic linkage torsion is discussed in detail. The selective interaction between the transition metal ion and the 7N site of the purine base is considered to be partly responsible for the stabilization of the base in a syn conformation, which favours the adoption by the polynucleotide (poly d(G-C), poly d(A-C).poly d(G-T) or poly d(A-T)) of a Z type conformation.

Cobalt↗
PubMed1971

Dose responsiveness and variation among inbred strains of mice in production of interferon after treatment with poly (I)-poly (C) (poly-D-lysine) complexes.

Poly-d-lysine forms a stochiometric complex with poly(I) . poly(C) which has a higher T(m) (83 C in 0.15 m NaCl) than the uncomplexed double-stranded polyribo-nucleotide (63 C). The complex was superior to poly(I) . poly(C) alone as an interferon inducer in vivo. Significant serum interferon titers were attained in Swiss mice during a 24-hr period after intraperitoneal injection of 10 to 300 mug of poly(I) . poly(C) [1.0 poly-d-lysine] complex, at concentrations of 100 to 1,000 mug/ml. The serum interferon responses (average and maximum titers) of a series of inbred strains of mice to a single intraperitoneal injection of 100 mug of complex decreased in the order: Swiss > DBA/2 > C3H > BALB/c > CF-1 > AKR, C57Bl/6, NZB > SJL > NZW and varied by a factor of approximately 100 from the most to the least responsive.

Animals↗
PubMed1996

Enhancement of the mechanical properties of polylactides by solid-state extrusion. II. Poly(L-lactide), poly(L/D-lactide), and poly(L/DL-lactide.

Polylactides with various degrees of chain regularity-crystalline poly(L-lactide); amorphous poly(L/D-lactide), and amorphous poly(L/DL-lactide)-were processed into high-strength, high-modulus resorable rods using solid-state extrusion through a conical die. The rods with a highly fibrillated structure had flexural strengths at a yield of up to 215 MPa and flexural modulus of up to 13.7 GPa. The initially amorphous poly(L/DL-lactide) developed approximately 25% of crystallinity after solid-state extrusion. Poly(L/D-lactide) remained amorphous independently of the treatment procedure applied. The shear strengths, flexural strengths, and flexural moduli of the solid-state extruded rods increased with increasing draw ratio. For the semicrystalline materials, solid-state extrusion enhanced the crystallinity. The achievable draw ratios during solid-state extrusion, and in consequence the final mechanical properties, were lower for poly(L/D-lactide) and poly(L/DL-lactide) than for poly(L-lactide).

Calorimetry, Differential Scanning↗
PubMed1999

A DSC study of the miscibility of poly(ethylene oxide)-block-poly(DL-lactide) copolymers with poly(DL-lactide).

The purpose of this study was to examine the miscibility of poly(ethylene oxide)-block-poly(DL-lactide) copolymers with poly (DL-lactide). The copolymers L7E73L7 and L17E78L17 (L = carbonyloxymethylmethylene unit, OCOCH(CH3); E = oxyethylene unit, OCH2CH2) were synthesised by non-catalysed anionic polymerisation and characterised by gel permeation chromatography and 13C NMR. Blends of each of the copolymers with poly(DL-lactide) with compositions over the range from 10 to 90 wt% copolymer were cast as thin films and examined by differential scanning calorimetry (DSC) to determine glass transition temperatures (Tg) and melting temperatures (Tm). The phase diagram showed a region of miscibility above the melting point of the copolymer in the system (approx. 35-40 degrees C). Within this region the system was glassy at low mass fractions of oxyethylene in the copolymer (wE < or = 0.1) and rubbery at higher mass fractions. Below Tm a mechanically compatible glassy blend existed at low wE whilst quenching of systems of higher wE led to phase separation, the biphasic region consisting of crystalline Em-sequences of copolymer separated from non-crystalline poly(DL-lactide). The phase diagram resulting from this study provides the means for the design of drug delivery systems based on blends of poly(DL-lactide) and poly(ethylene oxide)-containing components. The crystal melt boundary can be lowered by the use of block copolymers with short poly(ethylene oxide) blocks permitting the preparation of blends which are miscible at room temperature and rubbery or glassy according to composition.

Biocompatible Materials↗
PubMed1984

Comparison of the conformation of poly(dI-dC) with poly(dI-dbr5C) and the B and Z forms of poly(dG-dC). One- and two-dimensional NMR studies.

One- and two-dimensional nuclear Overhauser effects (2D NOE) have been used to compare the conformational properties of 60-80 base pair long duplexes of the synthetic DNA polymer poly(dI-dC) with those of poly(dI-dbr5C) and poly(dG-dC) in the B and Z conformations. Cross peaks in the 2D NOE spectra arising from proton-proton dipolar interactions which are more or less independent of the DNA conformation are used to assign the spectra of these molecules. Other cross peaks are sensitive to the conformational details, and these are used to make deductions about the average conformation in solution. The proton-proton interactions that give rise to the cross peaks in the 2D NOE spectrum of poly(dI-dC) are indicative of a B family conformation and rule out the possibility of some alternative conformations, including A, Z, alternating B, and left-handed B-DNA. The spectra are similar to those obtained from B-form poly(dI-dbr5C) and poly(dG-dC) but different from Z-form poly(dG-dC). Taken together, these results indicate that the solution conformation of poly(dI-dC) is not unusual but more closely resembles that of other B-form DNAs.

Carbohydrates↗
PubMedDate not supplied

Poly(ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] and poly(ethylene glycol) as candidate biomaterials: characterization and mechanical property study.

Poly(ester urethane)s with poly[(R)-3-hydroxybutyrate] (PHB) as the hard and hydrophobic segment and poly(ethylene glycol) (PEG) as the soft and hydrophilic segment were synthesized from telechelic hydroxylated PHB (PHB-diol) and PEG using 1,6-hexamethylene diisocyanate as a nontoxic coupling reagent. Their chemical structures and molecular characteristics were studied by gel permeation chromatography, 1H NMR, and Fourier transform infrared spectroscopy. Results of differential scanning calorimetry and X-ray diffraction indicated that the PHB segment and PEG segment in the poly(ester urethane)s formed separate crystalline phases with lower crystallinity and a lower melting point than those of their corresponding precursors, except no PHB crystalline phase was observed in those with a relatively low PHB fraction. Thermogravimetric analysis showed that the poly(ester urethane)s had better thermal stability than their precursors. The segment compositions were calculated from the two-step thermal decomposition profiles, which were in good agreement with those obtained from 1H NMR. Water contact angle measurement and water swelling analysis revealed that both surface hydrophilicity and bulk hydrophilicity of the poly(ester urethane)s were enhanced by incorporating the PEG segment into PHB polymer chains. The mechanical properties of the poly(ester urethane)s were also assessed by tensile strength measurement. It was found that the poly(ester urethane)s were ductile, while natural source PHB is brittle. Young's modulus and the stress at break increased with increasing PHB segment length or PEG segment length, whereas the strain at break increased with increasing PEG segment length or decreasing PHB segment length.

Biocompatible Materials↗
PubMedDate not supplied

[Dependence of the antiviral activity of the poly(G).poly(C) complex on the size of the continuous poly(C)segments].

Modification of poly(C) by various frequency treatment with adenosine non-complementary to guanosine has produced poly(G) X poly (C.A) complexes with continuous double-stranded areas the length of which is determined by C/A ratio. Studies of the antiviral activity of poly(G).poly(C,A) complexes with C/A from 10:1 to 90:1 and poly(G).poly(C) in vesicular stomatitis virus-infected chick embryo cell cultures and in experimental tick-borne encephalitis of mice demonstrated that the maximum activity is achieved at an average lengths of double-stranded areas of 90 nucleotide pairs. At the same time, a low but statistically significant antiviral activity is observed at a length of double-stranded areas of 10-30 nucleotide pairs.

Animals↗
PubMed2004

Na+ and Mg2+ ion effect on the stability of a poly I . poly A . poly I triple helix.

Differential UV spectroscopy was used to study the temperature dependence of the conformational equilibrium in aqueous poly I . poly A . poly I (A2I) solutions containing Na+ (0.1-2 M) and Mg2+ (10(-5)-0.005 M) ions. Over the whole range of the studied Na+ and Mg2+ concentrations, the heating-induced destruction of the triple A2I helix is actually the A2I --> A + I + I (3 --> 1) transition. The rise of the transition temperature with increasing Na+ and Mg2+ contents is well described by Manning's and the "ligand" theories, which makes it possible to estimate the linear charge density on the single-stranded poly I (xi = 1.9 +/- 0.1) and the Mg2+-A2I binding constant (K = 1,250 M(-1) for the zero degree of binding). An analytical expression has been obtained, which correlates the constants of Mg2+ binding to three- and single-stranded polynucleotides (K3 and K1, respectively) and the linear charge density on them. There are only minor distinctions between the K3 values for A2U and A2I because these polynucleotides have similar structures. The difference in the K1 values is also slight as single-stranded poly U, poly I, and poly A have similar conformations. Dependence of the conformational transition temperatures of two triple helices with changing Mg2+ concentration.

Adenosine↗
PubMed1989

Ultraviolet resonance Raman spectroscopy of distamycin complexes with poly(dA)-poly(dT) and poly(dA-dT): role of H-bonding.

Raman spectra are reported for distamycin, excited at 320 nm, in resonance with the first strong absorption band of the chromophore. Qualitative band assignments to pyrrole ring and amide modes are made on the basis of frequency shifts observed in D2O. When distamycin is dissolved in dimethyl sulfoxide or dimethylformamide, large (30 cm-1) upshifts are seen for the band assigned to amide I, while amides II and III shift down appreciably. Similar but smaller shifts are seen when distamycin is bound to poly(dA-dT) and poly(dA)-poly(dT). Examination of literature data for N-methylacetamide in various solvents shows that the amide I frequencies correlate well with solvent acceptor number but poorly with solvent donor number. This behavior implies that acceptor interactions with the C = O group are more important than donor interactions with the N-H group in polarizing the amide bond and stabilizing the zwitterionic resonance form. The resonance Raman spectra therefore imply that the distamycin C = O groups, despite being exposed to solvent, are less strongly H-bonded in the polynucleotide complexes than in aqueous distamycin, perhaps because of orienting influences of the nearby backbone phosphate groups. In this respect, the poly(dA-dT) and poly(dA)-poly(dT) complexes are the same, showing the same RR frequencies. Resonance Raman spectra were also obtained at 200-nm excitation, where modes of the DNA residues are enhanced. The spectra were essentially the same with and without distamycin, except for a perceptable narrowing of the adenine modes of poly(dA-dT), suggesting a reduction in conformational flexibility of the polymer upon drug binding.

Binding Sites↗