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D T Brown

Publications and source records attributed to D T Brown.

At least 109 records · Page 6Linked to original sources
PubMed1987

Organization of the Sindbis virus nucleocapsid as revealed by bifunctional cross-linking agents.

Purified Sindbis virus nucleocapsids were reacted with a variety of bifunctional protein-specific cross-linking agents. The products were analyzed in concentration-gradient polyacrylamide gels and amounts of various products determined. These studies indicated that available lysine residues within adjacent capsid proteins in purified intact nucleocapsids are separated by 6 A. The capsid proteins in intact nucleocapsids are cross-linked in a pattern predicted for discrete monomeric entities, rather than in dimeric or trimeric aggregates. Purified, soluble capsid protein exists in a conformation that differs from the arrangement of protein within nucleocapsids. These conformational differences suggest that topological changes may occur in the capsid protein during virus maturation. Cross-linked nucleocapsids that were treated with RNases resulted in the generation of RNA-free protein shells that retained hexagonal morphology, indicating that, together, the RNA and protein form the outer surface of the nucleocapsid. These data are used to produce a model of the Sindbis virus nucleocapsid in which the proteins are arranged quasi-equivalently in a T = 4 icosahedral shell.

Capsid↗
PubMed1987

Topological organization of Sindbis virus capsid protein in isolated nucleocapsids.

Sindbis virus nucleocapsids were isolated from mature virions by a two-step purification method. Detergent-treated virions were sedimented in sucrose gradients and the nucleocapsid peaks chromatographed on RNase-free Sephadex G-200. The purified nucleocapsids displayed several morphologies when examined in the electron microscope. These morphologies, and the results of double-angle shadowing, suggest that the core of this enveloped virus has the shape of a regular icosahedron with a triangulation number of 4. Peptide mapping of capsid protein obtained from nucleocapsids that had been radioiodinated by a variety of means, indicated that of the four tyrosine residues in the protein, only Tyr180 was exposed at the surface of the icosahedral structure. The other three residues were not exposed on the outer surface of the nucleocapsid shell, nor on the surface of capsid protein itself, implying that they were buried within the folded protein.

Capsid↗
PubMed1987

Stereophotogrammetric analysis of changes in body volume associated with the induction of anaesthesia.

Changes in the volume of the trunk were measured in seven supine patients, when anaesthesia was induced with thiopentone i.v. Stereo-photograms were taken before and after induction and measurements of volume calculated from contour plots of a reconstructed stereo image. The changes in volume of the visible part of the trunk were between -846 and +505 ml. No systematic change in total or lower trunk ("abdominal") volume was evident, but there was a significant negative linear relationship (r = -0.87) between upper trunk ("ribcage") volume change and obesity (expressed as actual weight/expected weight). Changes in volume were more evident in the upper parts of the supine subject, in both ribcage and abdomen (P less than 0.05).

Adult↗
PubMed1987

Naloxone does not influence breathing during isoflurane anaesthesia.

Naloxone influences ventilation, probably by an action on endogenous opioids, in several conditions in which ventilation is reduced or impaired. Ventilatory depression is a feature of anaesthesia; some of the actions of anaesthetic drugs have been attributed to endogenous opioids. Naloxone was given to two groups of patients to investigate the possibility that ventilatory depression might be reversed. Patients breathed isoflurane in oxygen (1.5% end-tidal) or isoflurane in 67% nitrous oxide in oxygen (0.75% end-tidal) which are approximately equivalent MAC values. Naloxone 2 mg, i.v. given during surgery had no influence on ventilation or ventilatory timing in either group.

Adult↗
PubMed1986

Morphology of staphylococcus bacteriophage P 1.

The group D staphylococcal phage P 1 was examined in the electron microscope after preparation by a variety of procedures. The virion was found to have an icosahedral capsid attached to a long contractile tail structure, the viral tail could be seen in partially contracted configurations. Morphological variants in the length of the sheath and needle were frequently found.

Capsid↗
PubMed1986

Extracellular localization of pokeweed antiviral protein.

Pokeweed antiviral protein is an enzyme of Mr 29,000 known to inactivate a wide variety of eukaryotic ribosomes. We have used electron microscopy to show that the antibody specific for the protein is bound within the cell wall matrix of leaf mesophyll cells from Phytolacca americana. Any penetration or breakage of the cell wall and membrane could allow the enzyme to enter the cytoplasm, where it is likely to inhibit protein synthesis in the damaged cell. We speculate that pokeweed antiviral protein is a defensive agent whose principal function is probably antiviral.

Depression, Chemical↗
PubMed1986

Sindbis virus-mediated cell fusion from without is a two-step event.

The process by which Sindbis virus induces the fusion of BHK-21 cells in monolayer cultures after exposure to low pH was examined. The fusion process was found to require an exposure to low pH followed by a return to conditions closer to neutral pH. The rate at which cells fused was affected by the pH to which the monolayers were exposed, subsequent to the initial exposure to acid conditions. Virus-mediated cell fusion was not observed if the virus-cell complexes were maintained at the acid pH required for membrane fusion.

Animals↗
PubMed1986

Exclusion of superinfecting homologous virus by Sindbis virus-infected Aedes albopictus (mosquito) cells.

The infection of tissue-cultured Aedes albopictus (mosquito) cells by an alphavirus ultimately results in a persistently infected cell population which can be maintained in the laboratory for years. One characteristic of this culture is that it will not support the replication of superinfecting homologous virus. We have previously shown that mosquito cells persistently infected with Sindbis virus produce an antiviral agent which when applied to uninfected mosquito cells suppresses Sindbis virus replication. The exclusion of virus replication in the antiviral-agent-treated cells is similar to the phenomenon of homologous interference described in alphavirus-infected vertebrate cells. In this study we examined the expression of homologous interference in three lines of mosquito cells and compared the expression of homologous interference to the effects of the antiviral activity. The cell lines were found to differ in their ability to express homologous interference, and evidence suggests that the mosquito cells may suppress replication by homologous interference or by the action of the antiviral agent.

Aedes↗
PubMed1985

Structure of the sea urchin U1 RNA repeat.

The genes coding for U1 RNA in the sea urchin L. variegatus are present in a 1400 base pair tandem repeat. One member of the repeat has been cloned and its sequence determined. The repeat unit contains a single copy of the gene for L. variegatus U1 RNA. This gene encodes an RNA which is 75% homologous to mammalian U1 RNA. The L. variegatus U1 RNA could assume a secondary structure similar to that proposed for other U1 RNAs. In addition the L. variegatus U1 RNA is precipitated by anti-SM and anti-RNP antisera. Analysis of the L. variegatus genomic DNA using the cloned U1 gene as a probe reveals a major and a minor type of repeat unit. The two repeated units are the same length but differ in a number of restriction enzyme sites clustered 200-500 bases down-stream from the gene. The monomer we have cloned and sequenced is a representative of the minor repeat. A sequence (GATAA) which is -41 to -37 bases 5' to the gene has homology to the putative RNA polymerase II promoter. Fifteen bases 3' of the gene is a sequence (CAAAGAAAGAAAA) which is very similar to the sequence found 3' of the sea urchin histone genes. The two Hha I, Hpa II and Ava I sites in the repeat are all unmethylated in sperm DNA.

Animals↗
PubMed1985

A study of mucus glycoproteins in secretory otitis media.

Rheologically active mucus glycoproteins (mucins) were isolated from the middle ear effusions of 282 patients (344 ears) with secretory otitis media. Middle ear mucins from those patients with no other associated pathology were compared biochemically and biophysically with mucins from patients where a specific associated pathology was present. The most striking biochemical variation was total carbohydrate content, which was lowest for mucins derived from purulent secretions in general (30.9%) and mucoid secretions from patients with cleft palates (32%). Furthermore, the carbohydrate content was correlated with the rheologic activity of reconstituted mucins, both in dilute solution and in the gel state. All mucins had high intrinsic viscosities, sensitive to ionic strength and the mucolytic N-acetylcysteine. Transport studies indicated that certain middle ear effusions, particularly those from patients with cleft palates, may not be cleared from the middle ear because of insufficient viscoelasticity.

Adolescent↗
PubMed1985

Morphology of pseudophakic precipitates on intraocular lenses removed from human patients.

Cellular precipitates on the surface of 52 intraocular lenses removed from human patients for various reasons from one week to five years following implantation were studied with cytologic techniques and scanning electron microscopy. A variety of cellular responses were characterized: mononuclear precipitates composed of lymphocytes and macrophages, multinucleated giant cells, and a fibroblastic proliferation. Polymorphonuclear leukocytes were encountered less frequently. Acellular membranous precipitates were also observed. Cellular response was related to clinical history to correlate temporal and possible etiopathogenic factors in the formulation of these precipitates and their possible relationship to implant failure.

Chemical Precipitation↗
PubMed1985

Gliding movement of and bidirectional transport along single native microtubules from squid axoplasm: evidence for an active role of microtubules in cytoplasmic transport.

Native microtubules prepared from extruded and dissociated axoplasm have been observed to transport organelles and vesicles unidirectionally in fresh preparations and more slowly and bidirectionally in older preparations. Both endogenous and exogenous (fluorescent polystyrene) particles in rapid Brownian motion alight on and adhere to microtubules and are transported along them. Particles can switch from one intersecting microtubule to another and move in either direction. Microtubular segments 1 to 30 microns long, produced by gentle homogenization, glide over glass surfaces for hundreds of micrometers in straight lines unless acted upon by obstacles. While gliding they transport particles either in the same (forward) direction and/or in the backward direction. Particle movement and gliding of microtubule segments require ATP and are insensitive to taxol (30 microM). It appears, therefore, that the mechanisms producing the motive force are very closely associated with the native microtubule itself or with its associated proteins. Although these movements appear irreconcilable with several current theories of fast axoplasmic transport, in this article we propose two models that might explain the observed phenomena and, by extension, the process of fast axoplasmic transport itself. The findings presented and the possible mechanisms proposed for fast axoplasmic transport have potential applications across the spectrum of microtubule-based motility processes.

Animals↗
PubMed1985

BHK cells expressing Sindbis virus-induced homologous interference allow the translation of nonstructural genes of superinfecting virus.

The process by which Sindbis virus excludes superinfecting homologous virus was investigated with the use of temperature-sensitive mutants. Mutants in two RNA-negative complementation groups were found to be defective in their ability to establish interference at the nonpermissive temperature. These mutants were unable to establish interference in a mixed infection (complementation), suggesting that both were defective in a common gene product. Homologous interference was found to block the replication of superinfecting virus after attachment, penetration, and translation of the nonstructural genes encoded in the virus RNA. The production of nonstructural gene products of superinfecting wild-type virus was found to enhance the replication of certain RNA- temperature-sensitive interfering viruses at the permissive and the nonpermissive temperature. The ability of certain RNA- mutants to establish homologous interference and to demonstrate enhanced growth after superinfection with wild-type virus was interpreted to produce a model implicating both virus and host components in the establishment of homologous interference and in the replication of Sindbis virus RNA.

Animals↗
PubMed1985

Changes in the levels of three different classes of histone mRNA during murine erythroleukemia cell differentiation.

We used a gene-specific S1 nuclease assay to study the changes in steady-state mRNA levels of several core histone variants during the differentiation of murine erythroleukemia cells. These studies allowed us to distinguish three distinct expression classes of histone genes. The expression of the major replication-dependent class of histone genes was tightly linked to DNA synthesis. The concentrations of these transcripts decreased rapidly as cell division slowed during the process of differentiation. In contrast, the replication-independent H3.3 transcript levels were constitutively maintained throughout differentiation and were unaffected by inhibitors of DNA or protein synthesis. We also identified among the cloned histone genes used as probes a third expression class, the partially replication-dependent variants. Expression of these transcripts became transiently uncoupled from the reduced rate of DNA synthesis accompanying the early stages of differentiation. We show that their synthesis is sensitive to the DNA synthesis inhibitor hydroxyurea but that selective uncoupling from DNA synthesis of these histone mRNAs occurs at a specific stage of differentiation. We present several hypotheses to explain how this might be accomplished. The expression characteristics of the mRNAs studied coincided with those of the proteins for which they code, indicating that changes in the relative levels of the different variants is mediated at least in part by changes in mRNA levels.

Animals↗
PubMed1985

Mucociliary transport of human ear secretions in otitis media with effusion.

Rheologically active mucus glycoproteins (mucins) were isolated from the middle ear effusions of 282 patients (344 ears) presenting with secretory otitis media (SOM). The mucins were pooled according to the pathologic condition associated with the SOM. Pools were reconstituted to the same conditions and tested for ciliary transport rates with the use of the frog palate transport model. Mucin obtained from cleft palate patients showed significant differences in transport behavior in comparison with mucins from other groups of patients with SOM.

Adolescent↗
PubMed1984

Rheological properties of living cytoplasm: a preliminary investigation of squid axoplasm (Loligo pealei).

A magnetic sphere viscoelastometer has been developed to perform rheological experiments in living axoplasm of Loligo pealei. The technique includes the use of a calibrated magnetic sphere viscoelastometer on surgically implanted ferro-magnetic spheres in intact squid giant axons. The axoplasm was discerned to be "living" by the biological criterion of tubulovesicular organelle motility, which was observed before and after experimentation. From these in vivo experiments, new structural characteristics of the axoplasm have been identified. First, analysis of magnetic sphere trajectories has shown the axoplasm to be a complex viscoelastic fluid. Directional experimentation showed that this material is structurally anisotropic, with a greater elastic modulus in the direction parallel to the axon long axis. Second, both magnetic sphere and in vivo capillary experiments suggested that the axoplasm is tenaciously anchored to the axolemma. Third, it was found that axoplasm could be modelled as a linear viscoelastic material in the low shear rate range of 0.0001 to 0.004 s-1. The simplest mechanical model incorporating the discovered properties of the material in this range is Burger's model.

Animals↗