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At least 145 records · Page 8Linked to original sources

PubMed1992

Removable magnetic dental attachment that permits magnetic resonance imaging.

Magnetic dental attachments cause magnetic resonance image (MRI) degradation. A new magnetic dental attachment that allows removal of magnetic parts to exchange them for nonmagnetic parts was developed and tested. It allows high quality MRI with no change in occlusal vertical dimension. A volunteer test subject with combinations of attachments in place was examined by MRI. The images produced showed no degradation or distortion. Magnetic attachments for overdentures or maxillofacial prostheses should be removable to permit use of MRI.

Cobalt↗

PubMed1990

Donor-specific tolerance permits burn allografting without increased sepsis.

Early excision and allografting of massive burns is beneficial. However, chronic immunosuppression, utilized to prolong allograft survival, increases the potential risk of infection. We have previously shown long-term skin allograft survival in mice with a 30% total body surface area (TBSA) burn by inducing donor-specific tolerance (DST) using only perigrafting administration of antithymocyte globulin (ATG) and donor bone marrow (DBM). Chronic immunosuppression is avoided. This study tests whether induction of DST compromises host resistance to infection. Resistance to a septic challenge created by cecal ligation and puncture (CLP) 10 days after a 30% TBSA burn was investigated in the following groups of mice: [table: see text] Positive blood cultures were documented for 97% of mortalities. Burn excision and grafting significantly (P less than or equal to 0.05) decreased mortality. No increased mortality was seen in allografted mice receiving ATG or ATG and DBM compared to isografted mice receiving no immunosuppression. These studies suggest that skin allografting with DST may permit the benefits of burn excision without the risks of infection seen with chronic immunosuppression.

Animals↗

PubMed1990

Composition of the gum from Combretum paniculatum and four other gums which are not permitted food additives.

Only three gum exudates are permitted for pharmaceutical and food use by international regulatory authorities, viz. gum tragacanth (Asiatic Astragalus spp.), gum karaya (Sterculia spp.) and gum arabic [Acacia senegal (L.) Willd.], but a wide range of other tree exudates is used for a variety of uses in their countries of origin. This paper presents analytical data for the gum exudates from Atalaya hemiglauca, Cassine aethiopica, Combretum paniculatum, Sclerocarya birrea, and Pseudocedrela kotschyi. These gums may have local technological applications, but are not recommended for addition to foodstuffs.

Amino Acids↗

PubMed1982

Adaptation in bacterial chemotaxis: CheB-dependent modification permits additional methylations of sensory transducer proteins.

Sensory transduction in E. coli consists of two phases, excitation and adaptation, both of which involve the methyl-accepting chemotaxis proteins (MCPs). These molecules relay transmembrane signals and are reversibly methylated during adaptation of E. coli to environmental stimuli. Each MCP contains multiple sites of methylation, and we identified six of these sites in MCPI. Recently, a second covalent modification of MCPs has been identified, which is not methylation. This modification, designated CheB-dependent modification, is stimulated by repellents and causes a net increase in the negative charge of MCPI and MCPII by one or two charges. We demonstrate that one CheB modification occurs on the methyl-accepting methionine-and lysine-containing tryptic peptide in MCPI and MCPII, and the second CheB modification is on an arginine-containing tryptic peptide. The CheB modification allows three additional methyl groups to be incorporated into the methyl-accepting methionine-lysine peptide, while not actually creating all of these methylation sites. The two CheB modifications occur sequentially. A possible mechanism by which CheB modification permits additional methylations and the role of CheB modification in bacterial chemotaxis are discussed.

Bacterial Proteins↗

PubMed1986

Chromosomal position or virus mutation permits retrovirus expression in embryonal carcinoma cells.

Retrovirus expression is restricted in embryonal carcinoma (EC) cells. To study how a virus can overcome this block, we selected and analyzed rare proviruses that are expressed in F9 cells. Our results indicate that provirus expression occurs by two different mechanisms: one provirus acquired a single base pair mutation in the retrovirus tRNA primer binding site, permitting provirus expression; expression of three proviruses was mediated by 5'-flanking DNA sequences. Surprisingly, five proviruses in 17 selected cell lines integrated into the same two distinct chromosomal regions, suggesting that the number of chromosomal positions in the cellular genome that allows virus expression is very limited. Our results suggest that genomic sequences that are actively transcribed in EC cells can be isolated by selection for retrovirus expression.

Base Sequence↗

PubMed1979

Testing of some permitted food colours for the induction of gene conversion in diploid yeast.

12 permitted food colours in use were screened for geno-toxicity. Mitotic gene conversion in Saccharomyces cerevisiae was used as the end-point. Each food colour was tested in stationary-phase as well as log-phase cells but without microsomal activation. These food colours did not cause any increase in mitotic gene conversion in diploid yeast BZ 34.

Drug Evaluation, Preclinical↗

PubMed1991

Does antibody-dependent epitope masking permit progressive tumour growth in the face of cell-mediated cytotoxicity?

It is not clear how immunogenic tumours can grow from small inocula in syngeneic hosts that mount both T-cell and B-cell responses. In this article Lionel Manson argues that antibody coats the tumour cells, protecting them from attack by cytotoxic lymphocytes, and thus permits the tumour to continue to grow and overwhelm the host. These observations may explain the paradox that an immunogenic tumour overwhelms the tumour-bearing host in the face of an ongoing anti-tumour immune response.

Animals↗

PubMed1986

Spin-labeling of influenza virus hemagglutinin permits analysis of the conformational change at low pH and its inhibition by antibody.

To study the conformational changes in the hemagglutinin (HA) molecule of A/seal/Mass/1/80 (H7N7) (Seal) influenza virus at low pH, a spin-labeling method was used. This method also permits study of antibody interaction with the HA. A synthetic nitroxide compound was used for spin-labeling of tyrosine residues of the isolated HA molecule. Electron spin resonance (ESR) spectra of the spin-labeled HA at various pH values indicated that a conformational transition occurred under acidic conditions, and around pH 5.8 the HA molecule has maximal flexibility. Since virus-induced hemolysis occurs optimally at pH 5.8-5.9, the HA molecule in the maximally flexible conformation is considered to mediate membrane fusion. The ESR spectra of the antibody-bound HA at various pH values revealed that monoclonal antibodies to different regions on the molecule may inhibit the conformational change by different modes. One antibody inhibited the changes in the HA that resulted in flexibility, while the other did not. These results support the assumption that monoclonal antibodies, which failed to inhibit hemagglutination of the virus yet neutralized viral infectivity, inhibited the fusion step in the viral replication process by interfering with a low pH-induced conformational change in the HA molecule (Kida, H., Webster, R.G. and Yanagawa, R. (1983) Arch. Virol. 76, 91-99).

Animals↗

PubMed1990

Toxicological evaluation of food additives. Toxicological evaluation over estimation of potential high intake to permitted levels of use of food additives and vice versa.

Permitted levels of use for food additives should agree with the acceptable daily intakes (ADIs) established by toxicologists. To ensure accordance, nutritional and physiological factors can be used to estimate high intakes of food and beverages. Appetite and thirst (energy and liquid requirements) are such quantitative factors. They are universal and, if placed on the same level as the ADI, i.e., expressed on a kilogram of body weight basis, can be used to estimate high intakes of an additive. This tool can be easily used to judge whether a suggested level of use may cause consumption of the additive to exceed the ADI. It also tells us to what level (ADI) toxicological clearance should be sought, when the technological need is known. The method is independent of food consumption surveys, but these may be carried out to confirm its forecasts. This paper uses caramel in soft drinks as an example. The approach, also called "the budget method," has been tried out in Denmark and Sweden. It is now being offered as a solution to the problem facing the European Communities: to establish before 1993 a common list of food additives containing quantitative limitations for use.

Appetite↗

PubMed1990

Intracellular labeling of dentate granule cells in fixed tissue permits quantitative analysis of dendritic morphology.

Although cortical neurons in fixed tissue can be labeled by intracellular dye injection, it is not yet known whether the dye diffuses to the most distal tips of the dendrites, or whether all dendritic branches of a neuron are labeled. In this study we addressed these questions by injecting granule neurons from the rat dentate gyrus in fixed, 400-microns-thick hippocampal slices with the fluorescent dye Lucifer yellow and comparing the resultant dendritic morphologies with those of neurons labeled in slices maintained in vitro. Results indicated that each dendritic branch was filled to its most distal tip and that the average number of branches per neuron in the fixed tissue was the same as that seen after in vitro labeling. Thus, intracellular labeling of neurons in fixed tissue permits quantitative studies of dendritic tree structure.

Animals↗

PubMed1991

Mutations permitting the anaerobic growth of Escherichia coli on trehalose.

Wild-type strains of Escherichia coli K-12 do not grow anaerobically on trehalose or galactose. We isolated two operon fusion mutants of E. coli which gained the ability to grow on trehalose anaerobically (tan). The tanA-lac mutation was located at 41 min on the E. coli genetic map and also abolished growth on glucuronic acid both aerobically and anaerobically. The tanB-lac mutation was mapped to 68 min and permitted anaerobic growth on galactose as well as trehalose. The tanB-lac fusion was induced anaerobically whereas tanA-lac showed more or less constitutive beta-galactosidase expression.

Anaerobiosis↗

PubMed1985

An Escherichia coli recBCsbcBrecF host permits the deletion-resistant propagation of plasmid clones containing the 5'-terminal palindrome of minute virus of mice.

The deletion events that have plagued attempts to maintain molecular clones with long palindromic DNA sequences in Escherichia coli have been shown to be less frequent in recBCsbcB hosts [Collins et al., Gene 19 (1982) 139-146]. This study sought to determine if such hosts would permit the stable propagation of plasmid clones carrying the deletion-generating, 206 nucleotide (nt) long, imperfect palindrome derived from the 5' terminus of the genome of minute virus of mice (MVM), an autonomous parvovirus [Astell et al., Nucleic Acids Res. 11 (1983) 999-1018]. To this end these hybrid plasmids were used to transform several different mutant recBCsbcB hosts, followed by the isolation and restriction mapping of plasmid DNA from selected transformants. Characterization of plasmid DNA isolated from a recBCsbcBrecF host indicated deletion-resistant propagation of the intact species. Sequence analysis of unamplified and chloramphenicol (Cm)-amplified plasmid DNA obtained from these clones confirmed the integrity of the palindromic region of the viral DNA insert.

Base Sequence↗

PubMed1986

A plasmid expression vector that permits stabilization of both mRNAs and proteins encoded by the cloned genes.

Two new expression vectors have been constructed to take advantage of several useful properties of bacteriophage T4-infected Escherichia coli. These plasmids, pRDB8 and pRDB9, contain the promoter region and start codon of T4 gene 32, a contiguous multiple cloning site (MCS), and translation and transcription termination signals. DNA fragments inserted into the MCS are transcribed and translated at a high level in both uninfected and phage T4-infected cells. Furthermore, the extreme stability of the hybrid mRNA after infection permits the specific biosynthetic labeling of the protein encoded by the cloned gene. In addition, the cloned gene product is stabilized, since the host-mediated degradation of foreign proteins is inhibited by phage infection. The properties of this expression system were demonstrated with the constant region of a rabbit immunoglobulin lambda light chain (C lambda) gene. Although proteolytic degradation of the C lambda fusion protein was rapid in uninfected cells, degradation was blocked in phage-infected cells and the protein accumulated in greater amounts.

Base Sequence↗

PubMed1988

Expression vectors permitting cDNA cloning and enrichment for specific sequences by hybridization/selection.

A set of vectors is described which allow the efficient cloning of full-length cDNAs, using a modification of the method of Okayama and Berg [Mol. Cell Biol. 2 (1982) 161-170], and enrichment of specific sequences directly from cDNA libraries by hybridization/selection. The vectors pcDpolyB+ and pcDpolyB- are derived from an expression vector described previously [Okayama and Berg, Mol. Cell Biol. 3 (1983) 280-289] and allow expression of cloned cDNAs in eukaryotic cells from the simian virus 40 early region promoter. The vectors BSB+ and BSB- contain convenient priming sites for sequence analysis and the T3 and T7 RNA polymerase promoters, allowing synthesis of transcripts homologous to either strand of the cDNA. Each of these vectors also contains the intergenic region from the bacteriophage f1 permitting synthesis of single-stranded (ss) copies of the cDNA libraries. Enrichment for cDNAs containing sequences homologous to the hypoxanthine phosphoribosyl transferase gene from an ss copy of a cDNA library by hybridization/selection is demonstrated. Levels of enrichment sufficient for the direct cloning of specific sequences without requiring colony or plaque hybridizations were obtained. Libraries constructed from different cell types can be screened against each other to create sublibraries highly enriched in sequences specific to a single cell type. The availability of cDNA expression libraries enriched for cell-type-specific cDNAs should greatly enhance the efficiency with which cDNAs can be identified on the basis of functional assays.

Cloning, Molecular↗

PubMed1989

Vectors permitting visual monitoring of simple transposition events.

The construction and use of two novel transposon(Tn)-delivery vectors is described. These vectors carry Inc.W or Inc.N broad-host-range transfer functions cloned next to the narrow-host-range replicon of pBR329. The host specificities of pSLX10 and pSLX23 both complement and extend the host specificities of existing Tn delivery vectors. Plasmids pSLX10 and pSLX23 were shown to transfer at high frequency in intergeneric matings. The lux genes which are present on each vector permit the visual monitoring of transconjugants which have retained a Tn element, but are devoid of plasmid molecules. pSLX10 and pLSX23 were efficiently used to generate a range of auxotrophic mutants in various strains of Pseudomonas as well as to clone genes from Serratia liquefaciens. These vectors may have general applicability to identify and clone genes in a wide range of Gram-negative bacteria.

Bacterial Proteins↗

PubMed1996

Two versatile eukaryotic vectors permitting epitope tagging, radiolabelling and nuclear localisation of expressed proteins.

Two versatile eukaryotic expression vectors have been developed which permit the production of an epitope-tagged cDNA insert by transient transfection in mammalian cells or by in vitro transcription-translation. The first vector, pCATCH, can be used to clone cDNA inserts in three different frames via eight unique restriction sites in a multiple cloning site (MCS) located downstream from both the FLAG epitope and the specific heart muscle kinase phosphorylation site, conferring the possibility of in vitro radiolabelling. A specific protease cleavage site enables the removal of the FLAG epitope, simplifying affinity purification of recombinant CATCH proteins. pCATCH possesses stop codons in all three reading frames at the 3' terminal end of the MCS. A derivate of this vector, pCATCH-NLS, was constructed by incorporating an SV40 nuclear localisation signal upstream from the MCS, for directed localisation of the tagged proteins.

Amino Acid Sequence↗

PubMed1995

Cyclophosphamide immunosuppression does not permit successful myoblast allotransplantation in mouse.

Cyclophosphamide immunosuppression does not permit successful myoblast allotransplantation in mouse. Myoblast transplantation is a potential treatment for Duchenne muscular dystrophy. In one clinical trial, Duchenne patients were immunosuppressed with cyclophosphamide. We report here that myoblasts from transgenic mice expressing the beta-galactosidase reporter gene transplanted in mdx mice failed to form new muscle fibres when cyclophosphamide (2 or 10 mg kg-1 per day) was used for immunosuppression. At the lowest dose of cyclophosphamide (2 mg kg-1 per day), some mdx recipient mice formed antibodies against donor myoblasts; however, no humoral immune reaction was observed at the highest dose (10 mg kg-1 per day). The failure of transplantation under cyclophosphamide treatment was attributed to the low immunosuppressive activity at a low dose and to the toxic action of a high dose of this drug. These results could explain the lack of success of myoblast transplantation in a previous clinical trial.

Animals↗

PubMed1995

Low avidity recognition of self-antigen by T cells permits escape from central tolerance.

The immunodominant epitope of myelin basic protein, Ac1-9, is encephalitogenic in H-2u mice. We have previously demonstrated that this epitope displays low affinity for I-Au and have suggested that the avidity of T cell recognition in the thymus may be compromised, enabling autoreactive T cells to escape self-tolerance. We have addressed this hypothesis directly by constructing transgenic mice expressing an encephalitogenic T cell receptor (TCR). Parenteral administration of Ac1-9 had no discernable impact on developing thymocytes. In contrast, peptide analogs displaying far higher affinity for I-Au, provoked deletion of CD4+ CD8+ cells and transient down-regulation of the TCR by mature CD4+ CD8- thymocytes. The use of analogs of intermediate affinity permitted a margin of error to be defined for the induction of tolerance and confirmed that the affinity of Ac1-9 lies well below the critical threshold.

Animals↗