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Polymer Formation (polymer + formation)
Selected AbstractsActin on DNA,An ancient and dynamic relationship,CYTOSKELETON, Issue 8 2010Kari-Pekka Skarp Abstract In the cytoplasm of eukaryotic cells the coordinated assembly of actin filaments drives essential cell biological processes, such as cell migration. The discovery of prokaryotic actin homologues, as well as the appreciation of the existence of nuclear actin, have expanded the scope by which the actin family is utilized in different cell types. In bacteria, actin has been implicated in DNA movement tasks, while the connection with the RNA polymerase machinery appears to exist in both prokaryotes and eukaryotes. Within the nucleus, actin has further been shown to play a role in chromatin remodeling and RNA processing, possibly acting to link these to transcription, thereby facilitating the gene expression process. The molecular mechanism by which actin exerts these newly discovered functions is still unclear, because while polymer formation seems to be required in bacteria, these species lack conventional actin-binding proteins to regulate the process. Furthermore, although the nucleus contains a plethora of actin-regulating factors, the polymerization status of actin within this compartment still remains unclear. General theme, however, seems to be actin's ability to interact with numerous binding partners. A common feature to the novel modes of actin utilization is the connection between actin and DNA, and here we aim to review the recent literature to explore how this connection is exploited in different contexts. [source] Effect of dewaxing pretreatment on composition and stability of rice bran oil: Potential antioxidant activity of wax fractionEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2006Samia Mezouari Abstract The effect of dewaxing pretreatment on rice bran oil composition and stability was investigated, as well as the possibility to use rice bran oil waxes as natural antioxidants at high temperatures. A correlation between wax content and dewaxing time was noticed. The pre-dewaxing process led to a loss of minor compounds, which negatively affected the oxidative stability index (OSI) of the dewaxed oil. The addition of rice bran oil waxes improved the oil stability index and heat stability of sunflower oil. An increase of 60% of the OSI and a significant decrease in polymer formation (59.2%) were observed. [source] Polymerization at the gas/solution interface: Preparation of polymer microstructures with gas bubbles as templatesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Maciej Mazur Abstract We report on the chemical polymerization of 2-methoxyaniline at the interface between an aqueous solution and air. The polymer is formed in the interfacial region, whereas the soluble trimer is yielded in the bulk of the polymerization solution. The preferential polymerization of 2-methoxyaniline is discussed in terms of monomer and oligomer accumulation at the interface, which influences the reactivity of these species and allows further polymerization. The phenomenon of polymer growth is employed to selectively deposit polymeric material onto glass slides decorated with gas microbubbles. Because of preferential polymerization at the bubble/solution interface, hemispherical features are produced on the surface of glass. When some polymeric material is mechanically removed, microrings or microholes are obtained. The anomalous polymerization of 2-methoxyaniline is compared to that of 2-methylaniline. This monomer polymerizes uniformly within the entire volume of the reaction mixture; thus, no preferential polymer formation at the gas/solution interface is observed. As a result, deposition on microbubble-decorated glass slides produces polymeric films containing a number of microholes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Phthalide as an activating group for the synthesis of poly(aryl ether phthalide)s by nucleophilic aromatic substitutionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2002Daniel M. Knauss Abstract The phthalide ring was examined as an activating group for nucleophilic aromatic substitution. The proposed mechanism by which activation occurs is through a ring opening of the phthalide ring to form a Meisenheimer-like , complex. 3,3-Bis(4-fluorophenyl)phthalide was synthesized and examined under different reaction conditions to determine its suitability for polymer formation. Semiempirical calculations at the PM3 level suggested that 3,3-bis(4-fluorophenyl)phthalide is only moderately activated, whereas 1H, 13C, and 19F NMR spectroscopy suggested that the monomer was not sufficiently activated for nucleophilic aromatic substitution. However, low-molecular-weight polymers (number-average molecular weight < 7000 g/mol) were produced from bisphenol A, hydroquinone, and phenolphthalein. The polymers were characterized by gel permeation chromatography, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, NMR spectroscopy, and differential scanning calorimetry. The polymers displayed relatively high glass-transition temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3046,3054, 2002 [source] Long-lived intermediates in reversible addition,fragmentation chain-transfer (RAFT) polymerization generated by , radiationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2002Christopher Barner-Kowollik Abstract A novel experimental procedure is presented that allowed probing of reversible addition,fragmentation chain-transfer (RAFT) free-radical polymerizations for long-lived species. The new experimental sequence consisted of gamma irradiation of a mixture of initial RAFT agent (cumyl dithiobenzoate) and monomer at ambient temperature, a subsequent predetermined waiting period without initiation source also at ambient temperature, and then heating of the reaction mixture to a significantly higher temperature. After each sequence step, the monomer conversion and molecular weight distribution were determined, indicating that controlled polymer formation occurs only during the heating period. The results indicated that stable intermediates (either radical or nonradical in nature) are present in such experiments because thermal self-initiation of the monomer can be excluded as the reason for polymer formation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1058,1063, 2002 [source] Synthesis, Characterization, and Mechanism of Polymerization of Poly(but-2-ene sulfide),MACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2004Subramanian Sundarrajan Abstract Summary: The effect of structural factors on polymer formation versus cyclization is reported. The reaction of sodium sulfide with either 1,4-dibromobut-2-ene 1 or 1,4-dibromobutane 2 has been carried out in presence of a phase transfer catalyst and it was observed that the former yields polymer, whereas the latter gives cyclic and linear products. Interestingly, trans/cis isomerization takes place during the polymer formation from 1 and a plausible mechanism has also been discussed. The reaction mechanism for unsaturated compound 1 and saturated compound 2 is discussed here. [source] Magnetic resonance imaging of spatially resolved acrylamide photopolymerizationMAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2003Tom J. Lees Abstract Magnetic resonance imaging was employed to examine spatially and temporally resolved photopolymerization of acrylamide gels. Fast exchange between free and bound water results in single exponential T2 decay, where 1/T2 scales linearly with polymer concentration. Measured T2s are sensitive to the experimental conditions; however, the 1/T2 relationship to polymer concentration allows a straightforward interpretation of image contrast changes during photopolymerization. The polymer appears to form at a nearly constant rate until the monomer concentration is significantly depleted. Conventional spin-echo images and quantitative CPMG-weighted spin-echo images were acquired. Photopolymerization of a partially masked sample produced a sharp transition (1 mm width) between polymer and monomer regions of the sample. The image intensity is uniform throughout the illuminated region of the sample, indicating uniform polymer formation. Interrupting the illumination quenches polymer formation. Copyright © 2003 John Wiley & Sons, Ltd. [source] A novel splice variant of the ,-tropomyosin (TPM2) gene in prostate cancerMOLECULAR CARCINOGENESIS, Issue 6 2010Stephen J. Assinder Abstract Decreased expression of high molecular weight isoforms of tropomyosin (Tm) is associated with oncogenic transformation and is evident in cancers, with isoform Tm1 seemingly an important tumor suppressor. Tm1 expression in prostate cancer has not previously been described. In this study, while demonstrating suppressed levels of Tm1 in the prostate cancer cell lines LNCaP, PC3, and DU-145 compared to normal prostate epithelial cell primary isolates (PrEC), a novel splice variant of the TPM2 gene was identified. Quantitative RT-PCR determined significantly greater levels of the transcript variant in all three prostate cancer cell lines than in normal prostate epithelial cells. Characterization of this novel variant demonstrated it to include exon 6b, previously thought unique to the muscle-specific ,-Tm isoform, with an exon arrangement of 1,2,3,4,5,6a,6b,7,8,10. Inclusion of exon 6b introduces a premature stop codon directly following the 6a,6b exon boundary. Western blot analysis demonstrated the presence of a truncated protein in prostate cancer cell lines that was absent in normal prostate epithelial cells. It is hypothesized that this truncated protein will result in suppression of Tm1 polymer formation required for actin filament association. The lack of Tm polymer,actin association will result in loss of the stable actin microfilament organization and stress fiber formation, a state associated with cell transformation. Mol. Carcinog. © 2010 Wiley-Liss, Inc. [source] F plasmid partition depends on interaction of SopA with non-specific DNAMOLECULAR MICROBIOLOGY, Issue 4 2008Jean-Philippe Castaing Summary Bacterial ATPases belonging to the ParA family assure partition of their replicons by forming dynamic assemblies which move replicon copies into the new cell-halves. The mechanism underlying partition is not understood for the Walker-box ATPase class, which includes most plasmid and all chromosomal ParAs. The ATPases studied both polymerize and interact with non-specific DNA in an ATP-dependent manner. Previous work showed that in vitro, polymerization of one such ATPase, SopA of plasmid F, is inhibited by DNA, suggesting that interaction of SopA with the host nucleoid could regulate partition. In an attempt to identify amino acids in SopA that are needed for interaction with non-specific DNA, we have found that mutation of codon 340 (lysine to alanine) reduces ATP-dependent DNA binding > 100-fold and correspondingly diminishes SopA activities that depend on it: inhibition of polymer formation and persistence, stimulation of basal-level ATP hydrolysis and localization over the nucleoid. The K340A mutant retained all other SopA properties tested except plasmid stabilization; substitution of the mutant SopA for wild-type nearly abolished mini-F partition. The behaviour of this mutant indicates a causal link between interaction with the cell's non-specific DNA and promotion of the dynamic behaviour that ensures F plasmid partition. [source] | |||||||||||||