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Biomedical subjects

W D Taylor

Publications and source records attributed to W D Taylor.

At least 37 records · Page 2Linked to original sources
PubMed1990

Homologous recombination and mutagenesis of gamma-irradiated plasmid DNA in Escherichia coli host cells.

Plasmid DNA was used to study gamma-radiation-induced recombination and mutagenesis in Escherichia coli host cells. Plasmid pBRP1, a derivative of pBR322 containing the lac operon of E. coli, was irradiated with 60Co gamma rays prior to transformation into E. coli strains of different recA and lac genotypes. Plasmid-chromosome recombination was assayed in lacY1 host cells, whereas plasmid mutagenesis was assayed in delta lac host cells lacking chromosomal sequences homologous to the plasmid. Both recombinant and mutant plasmids were identified by the phenotypic changes in lactose utilization, and confirmed by restriction analysis of isolated plasmids. Plasmid-chromosome recombination was induced to high levels (about 20% of survivors at 700 Gy) and was dependent on the host recA gene. Plasmid mutagenesis occurred at lower levels (about 1.5% of survivors at 600 Gy) and was relatively independent of the recA gene. Plasmid survival was unaffected by the presence or absence of host recA mutations or the potential for plasmid-chromosome recombination.

Cobalt Radioisotopes↗
PubMed1988

Expression of the rat growth hormone gene in transfected CV-1 cells.

Expression of the cloned rat growth hormone gene was studied in transfected CV-1 cells. Cell lines expressing rat growth hormone synthesized and secreted the 22 kilodalton form and the 20 kilodalton variant. The results confirm that the 20 kilodalton variant arises from an alternatively spliced mRNA rather than expression from a variant gene in rat. The 5' end of the mRNA from expressing cell lines was located upstream of the normal initiation site in rat. Transcription initiated within a 5' flanking AT rich sequence. Results presented indicate that transcription from normally silent promoter or promoter-like sequences dictated rat growth hormone gene expression in transfected cells. Finally, no hormone was expressed by CV-1 cells transfected with a plasmid containing the rat growth hormone gene in the same transcriptional reading frame as the neomycin resistance gene of pSV2neo indicating an effect of cloning orientation on expression in CV-1 cells.

Animals↗
PubMed1987

Alternative splicing model for the synthesis and secretion of the 20 kilodalton form of rat growth hormone.

The characterization of a 20 kilodalton (20 kD) variant of rat growth hormone is reported. The 20 kD variant from rat pituitary gland extracts was identified on Western immunoblots of polyacrylamide gels. It was also shown that pituitary tissue maintained in culture secretes the 20 kD form. A rat growth hormone cDNA fragment was used as a probe in S1 nuclease mapping experiments of rat pituitary poly (A) mRNA to detect the presence of two growth hormone mRNAs in the rat pituitary gland. The protected mRNAs correspond to the predicted sizes that would encode the 22 kD and 20 kD forms of growth hormone. The site of variation between the mRNAs maps to a potential alternative 3' splice site in the 5' end of exon 3 of the coding sequence. The results support the hypothesis that the 20 kD variant in rat is the product of an mRNA alternatively spliced in exon 3, as is the case for the human growth hormone.

Animals↗
PubMed1986

Reciprocal and non-reciprocal homologous recombination between Escherichia coli chromosomal DNA and ultraviolet light-irradiated plasmid DNA.

Plasmid DNA substrates were used to study ultraviolet (UV)-induced recombination events in Escherichia coli host cells. Plasmids derived from pBR322, containing all or part of the lac operon of E. coli, were irradiated with ultraviolet light before transformation into E. coli strains of different recA and lacY genotypes. Recombinational exchanges were identified by phenotypic changes in lactose utilization and were confirmed by restriction analysis of isolated plasmids. Ultraviolet-induced reciprocal plasmid-chromosome recombination occurred at a slightly higher frequency then non-reciprocal chromosome-to-plasmid recombination, and at a much higher frequency than non-reciprocal plasmid-to-chromosome recombination. These frequencies did not depend on segregative mechanisms. The asymmetry of non-reciprocal exchange was not due to the particular arrangement of wild-type and lacY1 alleles because the same results were observed when these were interchanged. The host recA gene was required for plasmid-chromosome recombination, and slightly enhanced plasmid survival. Evidence for plasmid replication prior to recombination was found in reciprocal recombinants, but rarely in the non-reciprocal recombinants analyzed. Irradiation of competent bacterial host cells prior to transformation did not effectively induce plasmid-chromosome recombination.

DNA, Bacterial↗
PubMed1985

Parvovirus infection in pigs with necrotic and vesicle-like lesions.

Porcine parvovirus was isolated from many visceral organs and also from the brain, serum and skin specimens of swine with vesicular-like conditions. Severe lesions were reported to have occurred in the mouth, on the tongue and snout, on the coronary band and in the interdigital spaces. Also, parvoviral antigens were demonstrated, by immunofluorescence, in the outer layers of hair follicles in skin adjacent to coronary band lesions.

Animals↗
PubMed1984

The fate and impact of oil and oil-dispersant mixtures in freshwater pond ecosystems: introduction.

Oil and oil-dispersant mixtures were added to the surface waters of a series of man-made ponds. The fate of the oil and dispersant (Norman Wells crude and Corexit 9527 respectively) were studied as well as the impact of the added chemicals on the ponds' ecosystems. Elements of the ecosystems studied include bacteria, fungi, phytoplankton, periphyton , proto- and mesozooplankton , zoobenthos and surface insects. In addition a number of water quality parameters were regularly monitored. Comparisons were made between oil-treated and control ponds, as well as oil-dispersant treated and oil and/or control ponds. This paper describes the experimental set up and provides a summary of the findings reported in the following five papers.

Animals↗
PubMed1984

Impact of oil and oil-dispersant mixtures on the fauna of freshwater ponds.

In a series of 5 artificial ponds, one was treated with a nomial concentration of 100 ppm of crude oil, two others were treated with a nominal 100 ppm of oil and 20 ppm of dispersant. Mesozooplankton populations were reduced in the oil-treated pond relative to the control pond, and eliminated in the oil-dispersant ponds. This condition persisted until the following year when the mesozooplankton was similar in all ponds. The protozooplankton experienced species shifts with Halteria and Strobilidium being eliminated initially in all treated ponds, but Halteria was collected in samples the following spring. Other protozoans such as thecamoebae increased in the treated ponds, while others, like zooflagellates , did not appear to be affected by the chemicals. Zoobenthos was affected by treatment, with the number of different types being reduced. The zoobenthos had recovered in one of the treated ponds the following spring, and that in the other treated ponds were recovering. Surface insects were eliminated after treatment, but recolonized during the next spring. Nekton were initially reduced by treatment. The population changes are discussed with respect to the fate of oil.

Animals↗
PubMed1984

Diffusion of a small molecule in the cytoplasm of mammalian cells.

Electron spin resonance was used to measure the diffusion of a small (Mr 170) spin label in the aqueous cytoplasm of mammalian cells. Translational and rotational motion were determined from the same spectra. Based on measurements made in model systems, it was hypothesized that calculations of the apparent viscosity from either rotational or translational motion would distinguish between the effects of cytoplasmic viscosity or cytoplasmic structure on diffusion. The diffusion coefficient calculated from spin label collision frequency, averaged 3.3 X 10(-6) cm2/sec in several cell lines. It was greater in growing cells and in cells treated with cytochalasin B than in quiescent cells. The viscosity of the cytoplasm calculated from the translational diffusion coefficient or the rotational correlation time was 2.0-3.0 centipoise (1 P = 0.1 Pa X sec), about 2-3 times that of the spin label in water. Therefore, over the dimensions measured by the technique, 50-100 A, solvent viscosity appears to be the major determinant of particle movement in cells under physiological conditions. However, when cells were subjected to hypertonic conditions, the translational motion decreased by 67%, while the rotational motion changed less than 20%. These data suggested that the decrease in cell volume under hypertonic conditions was accompanied by an increase in cytoplasmic barriers and a decrease in the spacing between existing components. In addition, a comparison of reported values for diffusion of a variety of molecules in water and in cells indicates that cytoplasmic structure plays an important role in the diffusion of proteins such as bovine serum albumin.

Animals↗
PubMed1984

Stimulation of recombination between homologous sequences on plasmid DNA and chromosomal DNA in Escherichia coli by N-acetoxy-2-acetylaminofluorene.

A plasmid containing a wild-type lac operon and a tetracycline-resistance gene was covalently modified by N-acetoxy-2-acetylaminofluorene and used to transform two series of Lac- Escherichia coli cell types. Each set contained wild-type and repair-deficient mutants. One set of cells contained a lacY mutation and the other a deletion of the entire lac operon. Survival and mutagenesis of the plasmid were measured as a function of the N-acetoxy-2-acetylaminofluorene concentration. The results indicate that when no homologous sequences are present in the chromosomal DNA, mutations occur at a low frequency: at 10% survival the frequency was 1-2 X 10(-4) mutants per transformant. When homologous sequences, the lacY allele, are present in the chromosomal DNA, Lac- plasmids are found at a high frequency in a recA-dependent, lexA-independent fashion: at 10% survival the frequency was 5-10 X 10(-2) mutants per transformant. Southern blot analysis of the restriction enzyme profiles of the resulting plasmid and host-cell DNA sequences showed recombinational transfer of host sequences to the N-acetoxy-2-acetylamino-fluorene-treated plasmid had occurred. When the host chromosomes contained Lac+ homologous sequences no mutants were found, indicating that the results were not caused by error-prone recombination.

2-Acetylaminofluorene↗
PubMed1982

Further evidence that ultraviolet radiation-enhanced reactivation of simian virus 40 in monkey kidney cells is not accompanied by mutagenesis.

Can simian virus 40 (SV40) be used to detect mutagenic DNA repair in cultured mammalian cells? The published evidence from different laboratories are in direct conflict. In order to decide between the conflicting evidence, we conducted experiments in two separate laboratories using experimental protocols similar to those previously used to investigate mutagenic repair with viral probes. Mutagenesis in SV40 virus stocks obtained by infecting ultraviolet (UV)-irradiated or unirradiated CV-1 monkey kidney cells with UV-irradiated or unirradiated temperature-sensitive SV40 mutant tsB201 was investigated. The frequency of reversion of the ts mutant to phenotypically wild-type virus was determined by assaying the virus stocks at permissive (33 degrees) and non-permissive (39 degrees) temperatures. These data show that (a) the reversion frequency for unirradiated virus propagated in irradiated cells was more than that in unirradiated cells; (b) irradiated virus gave more reversion than unirradiated virus in unirradiated and irradiated cells; and (c) irradiated virus had a lower reversion frequency in irradiated cells than in unirradiated cells. Reactivation experiments carried out in parallel; with the mutagenesis showed enhanced reactivation in UV-irradiated SV40 in UV-irradiated CV-1 cells. We conclude that enhanced reactivation of UV-irradiated SV40 was not mutagenic in monkey kidney cells.

Animals↗
PubMed1980

Characterization of the enzyme complex involving the folate-requiring enzymes of de novo purine biosynthesis.

Evidence is presented for a functional association of GAR TFase and the trifunctional protein within the protein complex consisting of GAR TFase, AICAR TFase, Ser HMase, and trifunctional protein. Resolution of the trifunctional protein from the remaining enzymes in the complex causes a loss of GAR TFase activity which is regained upon recombination. The minimum stoichiometry for GAR TFase reactivation is 3:1 GAR TFase--trifunctional protein. Determination by ultracentrifugation of the sedimentation coefficient as a function of protein concentration disclosed that the complex is in mobile equilibrium with the individual proteins. However, mixed GAR TFase--trifunctional protein species can be detected by trapping with cleavable bifunctional cross-linking reagents. Additional support for their interaction is found in the kinetic coupling of the trifunctional protein and GAR TFase activities that leads to a fourfold more efficient formation of formylglycinamide ribotide commencing with formate rather than with 5,10-methenyl-H4folate triglutamate.

Acyltransferases↗
PubMed1980

A comparison of herpes simplex virus plaque development after viral treatment with anti-DNA or antilipid agents.

The plaque development of Herpes simplex virus type 1 (HSV) is slower for viruses treated with two anti-DNA agents: ultraviolet radiation (UV) or n-acetoxy-2-acetyl-aminofluorene. For HSV treated with three antimembrane agents--butylated hydroxytoluene, acridine plus near UV radiation, or ether--the plaque development time is the same as for untreated viruses. These differences hold even for viruses that survived treatment that lowered viability below the 1% level. Gamma ray inactivation of HSV produces no change in plaque development even though this agent is believed to preferentially affect viral DNA.

2-Acetylaminofluorene↗