Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Assembly process”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,423 records · Page 79Linked to original sources
PubMed2005

Self-assembly of meso-tetrakis(4-N-ethylpyridiniurmyl) porphyrin and tetracarboxyl-phenyl calix[4]arene.

Novel dimeric capsules are generated from the noncovalent assembly of 5, 10, 15, 20-tetrakis(4-N-ethylpyridiniurmyl)prophyrin (TEPyP) and tetracarboxyl-phenyl calix[4]arene. The self-assembly system was investigated based on UV-Vis absorption and fluorescent spectra. The factors affecting the interaction process including pH and concentration were examined in detail. The association constants between TEPyP and calix[4]arene were determined by the nonlinear least squares fit. The results showed that the basic medium is favourable to the interaction and electrostatic interaction was determinate in the processes of self-assembly process. The related mechanism was discussed.

Calixarenes↗
PubMed1988

Analysis of the assembly of laminin and the laminin-entactin complex with laminin chain specific monoclonal and polyclonal antibodies.

Antibodies specific for the A, B1, and B2 chains of laminin have been obtained and characterized. Lam V, a rat X mouse monoclonal antibody, was obtained by immunizing Lewis rats with the extracellular matrix derived from the mouse endodermal line M1536-B3. The antibody was shown to recognize a conformation-sensitive epitope present on the A chain of laminin. The antibody exhibited high avidity for native laminin and uncomplexed newly synthesized laminin A chains. cDNA clones in the vector lambda-gt11 containing sequences for the B1 and B2 chains of laminin were shown to synthesize beta-galactosidase fusion proteins in the host cells induced with IPTG. The fusion protein F3 contained amino acid residues 822-1765 of the B1 chain of mouse laminin, and the fusion protein E4 contained 219 amino acids at the carboxyl terminus of the B2 chain of rat laminin. These two fusion proteins were used to obtain rabbit polyclonal antibodies which were characterized for their specificity and ability to immunoprecipitate laminin and the B chains of laminin. The chain-specific antibodies were used to analyze the assembly and processing of laminin in the mouse endodermal cell line M1536-B3. The results indicated that the covalent assembly of the A and B chains of laminin was initiated as early as 3 min after labeling cells. At this time point uncomplexed A chain of laminin could be observed even though there was an excess of B1 and B2 chains. As early as 4 min after labeling monomeric, dimeric, and oligomeric forms of the B chains of laminin were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

The exogenous pathway for antigen presentation on major histocompatibility complex class II and CD1 molecules.

The endosomes and lysosomes of antigen-presenting cells host the processing and assembly reactions that result in the display of peptides on major histocompatibility complex (MHC) class II molecules and lipid-linked products on CD1 molecules. This environment is potentially hostile for T cell epitope and MHC class II survival, and the influence of regulators of protease activity and specialized chaperones that assist MHC class II assembly is crucial. At present, evidence indicates that individual proteases make both constructive and destructive contributions to antigen processing for MHC class II presentation to CD4 T cells. Some features of CD1 antigen capture within the endocytic pathway are also discussed.

Animals↗
PubMed1989

Microcomputer processing of film radiographs.

An inexpensive image processing system, assembled from commercially available components and driven by "in-house" software, was tested as a means of processing radiographs obtained in a radiology department. In this preliminary study, the main interest was to investigate, through subjective appraisal, the ability of the system to recover the image quality of poorly exposed radiographs. Subsidiary objectives were to obtain some information regarding the specification limits of the system and its components, as well as some quantitative estimate of its advantages for clinical diagnosis. The system was used to process a set of film radiographs of an anthropomorphic chest phantom, produced under conditions that were designed to provide a wide range of image qualities. Following this, four sets of randomly ordered processed and unprocessed images were formally assessed by a group of experienced observers. Consensus opinion from the group indicated that significant improvement could be obtained through simple image processing. Some radiographs regarded as unacceptable became, after processing, acceptable to viewers.

Humans↗
PubMed1990

Synthesis and self-assembly of a functional monoclonal antibody in transgenic Nicotiana tabacum.

Immunoglobulin light and heavy chains are synthesized in mammalian cells as precursors containing a signal peptide. Processing and assembling result in formation of active antibodies. Chimeric genes have been made containing the coding sequence of the barley alpha-amylase signal peptide which has been fused to cDNAs coding for either the mature light or the mature heavy chain of a monoclonal antibody. A plasmid was constructed linking both chimeric genes under the control of plant active promoters in an expression cassette. This DNA fragment was stably integrated into the genome of Nicotiana tabacum by Agrobacterium tumefaciens mediated gene transfer. Synthesis of light and heavy chains and assembly to antibodies was detected in transgenic tobacco tissue using specific secondary antibodies. By electron microscopic immunogold labeling, the presence of assembled antibody could be detected within the endoplasmic reticulum. Affinity chromatography indicated biological activity of the assembled immunoglobulin produced in plant cells. Unexpectedly, a significant amount of assembled antibodies was found within chloroplasts.

Amino Acid Sequence↗
PubMed2006

3-O-(3',3'-dimethysuccinyl) betulinic acid inhibits maturation of the human immunodeficiency virus type 1 Gag precursor assembled in vitro.

3-O-(3',3'-Dimethysuccinyl) betulinic acid (PA-457) has been shown to potently inhibit human immunodeficiency virus (HIV) replication in culture. In contrast to inhibitors that act upon the viral proteinase, PA-457 appears to block only the final maturational cleavage of p25CA-p2 to p24CA. However, attempts to replicate this effect in vitro using recombinant Gag have failed, leading to the hypothesis that activity is dependent upon the assembly state of Gag. Using a synthesis/assembly system for chimeric HIV type 1 Gag proteins, we have replicated the activity of PA-457 in vitro. The processing of assembled chimeric Gag can be inhibited by the addition of drug with only the final cleavage of p25CA-p2 to p24CA blocked. Consistent with our hypothesis and with previous findings, inhibition appears specific to Gag assembled into an immature capsid-like structure, since synthetic Gag that remains unassembled is properly processed in the presence of the compound. To further analyze the authenticity of the assay, PA-457 was tested in parallel with its inactive parental compound, betulinic acid. Betulinic acid had no effect upon p25 processing in this system. Analysis of a PA-457-resistant mutant, A1V, in this system pointed to more rapid cleavage as a possible mechanism for resistance. However, characterization of additional mutations at the cleavage site and in p2 suggests that resistance does not strictly correlate with the rate of cleavage. With the establishment of an in vitro assay for the detection of PA-457 activity, a more detailed characterization of its mechanism of action will be possible.

Capsid Proteins↗
PubMed1996

Myosin drives retrograde F-actin flow in neuronal growth cones.

Actin filaments assembled at the leading edge of neuronal growth cones are centripetally transported via retrograde F-actin flow, a process fundamental to growth cone guidance and other forms of directed cell motility. Here we investigated the role of myosins in retrograde flow, using two distinct modes of myosin inhibition: microinjection of NEM inactivated myosin S1 fragments, or treatment with 2,3-butanedione-2-monoxime, and inhibitor of myosin ATPase. Both treatments resulted in dose-dependent attenuation of retrograde F-actin flow and growth of filopodia. Growth was cytochalasin sensitive and directly proportional to the degree of myosin inhibition, suggesting that retrograde flow results from superimposition of two independent processes: actin assembly and myosin-based filament retraction. These results provide the first direct evidence for myosin involvement in neuronal growth cone function.

Actins↗
PubMed2004

Formin is a processive motor that requires profilin to accelerate actin assembly and associated ATP hydrolysis.

Motile and morphogenetic cellular processes are driven by site-directed assembly of actin filaments. Formins, proteins characterized by formin homology domains FH1 and FH2, are initiators of actin assembly. How formins simply bind to filament barbed ends in rapid equilibrium or find free energy to become a processive motor of filament assembly remains enigmatic. Here we demonstrate that the FH1-FH2 domain accelerates hydrolysis of ATP coupled to profilin-actin polymerization and uses the derived free energy for processive polymerization, increasing 15-fold the rate constant for profilin-actin association to barbed ends. Profilin is required for and takes part in the processive function. Single filaments grow at least 10 microm long from formin bound beads without detaching. Transitory formin-associated processes are generated by poisoning of the processive cycle by barbed-end capping proteins. We successfully reconstitute formin-induced motility in vitro, demonstrating that this mechanism accounts for the puzzlingly rapid formin-induced actin processes observed in vivo.

Actins↗
PubMed1997

Ribosomal 5 S rRNA maturation in Saccharomyces cerevisiae.

The maturation of the ribosomal 5 S RNA in Saccharomyces cerevisiae is examined based on the expression of mutant 5 S rRNA genes, in vivo, and a parallel analysis of RNA processing, in vitro. Both types of analysis indicate that 5 S rRNA processing is not dependent on the nucleotide sequence of either the external transcribed spacer or the mature 5 S rRNA. The results further indicate the RNA is processed by an exonuclease activity which is limited primarily or entirely by helix I, the secondary structure formed between the mature and interacting termini. The 5 S RNA binding protein (YL3) also appears not to influence directly the maturation process, but rather to play a role in protecting the rRNA from further degradation by "housekeeping" nucleases. Taken together, the results continue to support a "quality control" function which helps to ensure that during maturation only normal precursors are processed and assembled into active ribosomes.

Nucleic Acid Conformation↗
PubMed1986

Fibrin assembly. Lateral aggregation and the role of the two pairs of fibrinopeptides.

The structural basis of the wide variability of the physical properties of fibrin clots and the process of assembly of the clot were investigated by electron microscopy of fibers formed under various ionic conditions. In addition, highly specific proteolytic enzymes from different snake venoms were used to remove selectively only the A (batroxobin) or the B (venzyme) fibrinopeptides from fibrinogen, in contrast to thrombin, which removes both pairs. Fibers produced by cleavage of only the B fibrinopeptides displayed a characteristic band pattern indistinguishable from that of fibers formed upon removal of either the A fibrinopeptides alone or of both pairs. Computer modeling studies suggest that there is a unique molecular packing that gives rise to this fibrin band pattern. These findings imply that the release of either fibrinopeptide triggers similar modes of aggregation; the intermolecular binding sites can be localized to particular molecular domains. The diameters of fibers formed with each condition of enzyme, pH, salt concentration, and temperature were measured from electron micrographs. All fibers, except for those produced at both high ionic strength and pH, had about the same average diameter of 85 +/- 13 nm. The degree of lateral aggregation of the fibers themselves varied greatly, however; fibers aggregated more readily with cleavage of both pairs of fibrinopeptides and at lower pH and salt concentrations. The formation of such thick fiber bundles increases the stability of the clot and its resistance to proteolytic dissolution.

Fibrin↗
PubMed2000

Like attracts like: getting RNA processing together in the nucleus.

Structures visible within the eukaryotic nucleus have fascinated generations of biologists. Recent data show that these structures form in response to gene expression and are highly dynamic in living cells. RNA processing and assembly require many factors but the nucleus apparently lacks any active transport system to deliver these to the RNAs. Instead, processing factors move by diffusion but are concentrated by transient association with functionally related components. At sites of high activity this gives rise to visible structures, with components in dynamic equilibrium with the surrounding nucleoplasm. Processing factors are recruited from this pool by cooperative binding to RNA substrates.

Animals↗
PubMed1983

Energetics and intermediates of the assembly of Protein OmpA into the outer membrane of Escherichia coli.

OmpA is a major protein of the outer membrane of Escherichia coli. It is made as a larger precursor, pro-OmpA, which requires a membrane potential for processing. We now show that pro-OmpA accumulates in the cytoplasm of cells treated with carbonyl cyanide m-chlorophenylhydrazone, an uncouple which lowers the membrane potential. Upon restoration of the potential, this pro-OmpA is secreted, processed, and assembled into the outer membrane. Pro-OmpA made in vitro is also recovered with the postribosomal supernatant. It is efficiently processed to OmpA by liposomes which have bacterial leader peptidase that is exclusively internally oriented. These experiments show that: (i) the insertion of pro-OmpA into the plasma membrane is not coupled to its synthesis; (ii) insertion is promoted by the transmembrane electrochemical potential; (iii) pro-OmpA can cross a bilayer spontaneously; and (iv) pro-OmpA is processed by the same leader peptidase which converts M13 procoat to coat.

Bacterial Outer Membrane Proteins↗
PubMed2001

Sucrase-alpha-dextrinase in the spontaneously diabetic BioBreed Wistar rat: altered intracellular carbohydrate processing.

Sucrase-alpha-dextrinase (S-D), a glycoprotein hydrolase in the border surface of the enterocyte, is altered in congenitally diabetic BioBreed Wistar (BB(d)) rats. Its intracellular assembly was examined in the current studies. Following pulse-chase experiments, S--D was specifically immuno-isolated from ER-Golgi and brush border membranes, and examined by SDS-PAGE and autoradiography. While synthesis and co-translational glycosylation of an immature species, P(i), in the ER proceeded normally, post-translational maturation of the N-linked carbohydrate chains was altered in the BB(d) rat. The mature species, P(m), was 10 kDa larger in BB(d) than in normal rats, and approximately 25% of its N-linked chains remained immature. The difference in mass was attributed to an appreciably larger mass of the O-linked chains of P(m) in BB(d) rats. In vivo kinetics of intracellular assembly displayed a delay in the appearance of P(m) in Golgi (Wistar, 15 min; BB(d), 30--60 min). These experiments, revealing structural alterations in congenital diabetes suggest an important role for intracellular glycosylation in the orderly assembly and processing of brush border S-D in the enterocyte.

Animals↗
PubMed1999

The possible role of colligin/HSP47, a collagen-binding protein, in the pathogenesis of human and experimental fibrotic diseases.

Colligin or heat shock protein 47 (HSP47) is a stress protein that resides in the endoplasmic reticulum and is thought to participate in intracellular processing, folding, assembly and secretion of procollagens. Irrespective of the tissue site and organ, induction of colligin/HSP47 expression is always noted during the process of fibrosis, particularly in and around the fibrotic lesions in both humans and experimental models. Its expression is highly tissue- and cell-specific, and restricted to mostly phenotypically altered collagen-producing cells. These observations suggest that upregulation of this collagen-specific chaperone-colligin/HSP47 may play an important role in the subsequent fibrotic process, possibly by regulating increased synthesis/assembly of collagens.

Animals↗
PubMed1987

Structure and assembly of desmosome junctions: biosynthesis, processing, and transport of the major protein and glycoprotein components in cultured epithelial cells.

Extracts of metabolically labeled cultured epithelial cells have been analyzed by immunoprecipitation followed by SDS-PAGE, using antisera to the major high molecular mass proteins and glycoproteins (greater than 100 kD) from desmosomes of bovine muzzle epidermis. For nonstratifying cells (Madin-Darby canine kidney [MDCK] and Madin-Darby bovine kidney), and A431 cells that have lost the ability to stratify through transformation, and a stratifying cell type (primary human keratinocytes) apparently similar polypeptides were immunoprecipitated with our antisera. These comprised three glycoproteins (DGI, DGII, and DGIII) and one major nonglycosylated protein (DPI). DPII, which has already been characterized by others in stratifying tissues, appeared to be absent or present in greatly reduced amounts in the nonstratifying cell types. The desmosome glycoproteins were further characterized in MDCK cells. Pulse-chase studies showed all three DGs were separate translation products. The two major glycoprotein families (DGI and DGII/III) were both found to be synthesized with co-translational addition of 2-4 high mannose cores later processed into complex type chains. However, they became endo-beta-N-acetylglucosaminidase H resistant at different times (DGII/III being slower). None of the DGs were found to have O-linked oligosaccharides unlike bovine muzzle DGI. Transport to the cell surface was rapid for all glycoproteins (60-120 min) as demonstrated by the rate at which they became sensitive to trypsin in intact cells. This also indicated that they were exposed at the outer cell surface. DGII/III, but not DGI, underwent a proteolytic processing step, losing 10 kD of carbohydrate-free peptide, during transport to the cell surface suggesting a possible regulatory mechanism in desmosome assembly.

Adenocarcinoma↗
PubMed1984

A system for the translation of receptor messenger-RNA and the study of the assembly of functional receptors.

The Xenopus oocyte translation system has been developed for the recognition of receptor messenger-RNA molecules. Observations with the nicotinic acetylcholine, GABA, glycine, glutamate and serotonin receptors show that the mRNAs coding for their subunits can be faithfully translated in the oocyte and the products processed, glycosylated, assembled to a receptor structure, inserted correctly in the cell membrane and organised to form the functional ion channel. The specific regulatory interactions between different sites on one receptor, as exemplified in the GABAA receptor, are established in this process. This system is of value for the detection of mRNAs for receptor gene cloning and for the study of receptor assembly and of the expression of multiple receptor genes. The receptor ion channels formed can also be studied in their own right in a highly accessible and controlled situation.

Acetylcholine↗
PubMed2006

Flexible solar-cell from zinc oxide nanocrystalline sheets self-assembled by an in-situ electrodeposition process.

Zinc oxide nanocrystalline sheets were self-assembled on a flexible polymer substrate to act as the electrode of dye-sensitized solar cells by an in situ-construction electrodeposition process. It was discovered that the nanosheet-based solar cell exhibited better performance than a nanoparticle-based solar cell or a well-oriented nanowire-based solar cell. The nanosheet microstructure has advantages which include the depression of loss during photoelectron transport, the increase of dye compound adsorption, and the enhance of incident light capture. As a result, the performance of dye-sensitized solar cells can be obviously improved. This success provides a feasible bottom-up approach for integrating a solar cell together with nanodevices and microcircuits on a flexible substrate which can work with self-supplied solar energy.

Electrochemistry↗
PubMed1997

Paraquat inhibits the processing of human manganese-dependent superoxide dismutase by SF-9 insect cell mitochondria.

Precursor human manganese-dependent superoxide dismutase (hMn-SOD) was expressed using the baculovirus system in Spodoptera fungiperda (Sf-9) insect cells. Following infection of Sf-9 cells with hMn-SOD-expressing baculovirus, mature hMn-SOD was expressed at 15-25% of total cellular protein, with the recombinant protein localized in the mitochondrial matrix. Partial amino acid sequencing and SOD activity assays indicated that the hMn-SOD was correctly processed and assembled by insect mitochondria. This expression system was used to study the effects of paraquat and menadione, two intracellular superoxide generators, on processing of precursor hMn-SOD by insect mitochondria. Paraquat was found to potently inhibit mitochondrial processing of hMn-SOD, leading to the accumulation of precursor hMn-SOD and a decrease in measurable Mn-SOD activity. In contrast, menadione treatment was not found to affect the ratio of precursor to mature Mn-SOD. Paraquat did not lead to lower total production of hMn-SOD or cellular toxicity at the concentrations which were found to block processing of precursor hMn-SOD. These results indicate that mitochondrial processing and import of the precursor protein hMn-SOD are early events susceptible to dysfunction induced by the redox-cycling agent paraquat. These results also emphasize that mitochondrial processing of precursor proteins represents a parameter of cellular function which may be compromised, preceding the appearance of more generalized deterioration of cellular function, under certain toxic or pathological conditions.

Animals↗