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R J Roberts

Publications and source records attributed to R J Roberts.

At least 163 records · Page 9Linked to original sources
PubMed1987

Genetic analysis of the 5-azacytidine sensitivity of Escherichia coli K-12.

DNA containing 5-azacytidine (5-azaC) has been shown to form stable detergent-resistant complexes with cytosine methylases. We reasoned that if 5-azaC treatment causes protein-DNA cross-links in vivo, then mutations in DNA repair and recombination genes may increase the sensitivity of a cell to 5-azaC. We found that although recA (defective) and lexA (induction-negative) mutants of Escherichia coli were very sensitive to the drug, mutations in uvrA and ung genes had little effect on cell lethality. The sensitivity of recA strains to 5-azaC was dose dependent and was enhanced by the overproduction of a DNA cytosine methylase in the cell. Unexpectedly, a strain of E. coli carrying a recA mutation and a deletion of the DNA cytosine methylase gene (dcm) was found to be significantly sensitive to 5-azaC. Study of mutations in the pyrimidine salvage pathway of E. coli suggests that direct phosphorylation of 5-azaC, rather than phosphorylation of its degradation products, is largely responsible for the lethal effects of the drug. The addition of uracil to the growth medium has little effect on cell lethality of recA mutants, but it partially reversed the inhibition of cell growth caused by 5-azaC. This reversal of the bacteriostatic effects of the drug could not be achieved by adding cytosine or orotic acid to the growth medium and required the presence of functional UMP-pyrophosphorylase (gene upp) in the cell.

Azacitidine↗
PubMed1987

Different functional domains of the adenovirus E1A gene are involved in regulation of host cell cycle products.

We have analyzed the cell cycle effects that different domains of the adenovirus E1A proteins have on quiescent primary BRK cells. Studies with deletion mutants that in combination removed all but the N-terminal 85 amino acids common to both the 12S and 13S proteins suggest that this region may be sufficient for the induction of synthesis of proliferating cell nuclear antigen and the stimulation of DNA synthesis. A second domain also common to the N-terminal exon of the 12S and 13S proteins was required for the induction of mitosis and stimulation of proliferation of primary BRK cells. A virus containing a mutation in this region was still able to stimulate DNA synthesis efficiently. A third domain, unique to the 13S protein, was required for the accelerated activation of the cellular thymidylate synthase gene in a manner similar to the 13S-dependent stimulation of adenovirus early region genes.

Adenovirus Early Proteins↗
PubMed1987

Comparison of the antioxidant properties of alpha-tocopherol and alpha-tocopheryl acetate in newborn rabbit lung.

The antioxidant properties of alpha-tocopherol and alpha-tocopheryl acetate in lung tissue were quantitated in vitro by measurement of thiobarbituric acid (TBA) reactants, pentane production and lipid peroxides following either an iron/ascorbate or a xanthine/xanthine oxidase oxidant stress. Lung homogenates were obtained from newborn rabbits treated intravenously with either 10 or 100 mg/kg of either alpha-tocopherol or alpha-tocopheryl acetate. The animals were killed 5 min after dosing to minimize the conversion of alpha-tocopheryl acetate to alpha-tocopherol. Lung homogenates from animals treated with alpha-tocopherol had decreased concentrations of TBA reactants and pentane production after incubation with either oxidant stress compared to lung homogenate from animals treated with alpha-tocopheryl acetate or vehicle alone. Lipid peroxide concentrations were no different in homogenates from alpha-tocopherol or alpha-tocopheryl acetate treated animals. Correlations between antioxidant activity and tissue concentrations of alpha-tocopherol indicate 50% inhibition is achieved with 30-100 micrograms/g lung tissue. In vitro addition of alpha-tocopherol required concentrations between 100 and 200 micrograms/g to reduce lipid peroxidation by 50%.

Animals↗
PubMed1987

Molecular basis of pulmonary oxygen toxicity.

There has been an explosion of knowledge pertaining to the generation and behavior of partially reduced oxygen metabolites--oxygen free radicals--in aqueous, in vitro systems; lacking is correlation of these intriguing findings to the biologically intact whole animal. Methodologies to study in vivo free radical-mediated processes are improving with the use of electron spin trapping of tissue samples, and in the future the precise role of oxygen radicals in oxygen injury may become clearer. With this new work with the chemistry and biochemistry of oxygen radicals, it is crucial to remember the special attributes of oxygen radical behavior in eukaryotic cells. There are many disparate compartments in cells that differ with respect to hydrophobicity, pH, and presence of iron salts and antioxidants. The ability of any oxygen radical; O2-, H2O2, .OH, to cause damage, will depend greatly on these and other factors. The final piece of the oxygen toxicity puzzle is the presence and activity of antioxidant substances, both enzymatic and nonenzymatic. Here again, compartmentalization is important. To provide beneficial protection, the antioxidant must be present in sufficiently high concentrations at the site of radical production or damage. In the special case of the premature infant who requires oxygen therapy, the balance between oxygen radical production and antioxidant capacities will determine whether oxygen injury ultimately occurs. The biologic uniqueness of the premature infant in regards to maturation and growth mandates investigations of these biochemical phenomena in appropriate experimental models, rather than extrapolation from studies conducted in adults and perhaps even full-term newborns.

Chemical Phenomena↗
PubMed1987

Pharmacology of vitamin E in the newborn.

The use of pharmacologic doses of vitamin E is distinctly different from nutritional vitamin E in regards to issues of efficacy and safety. Repeated administration of pharmacologic doses of vitamin E results in increasing concentrations of vitamin E in all tissues examined. The emergence of a toxic clinical syndrome associated with vitamin E therapy, the effects of vitamin E on important physiologic systems such as granulocyte function and the arachidonic acid cascade, the theoretic possibility of vitamin E becoming a prooxidant at high concentrations, and the continuing controversy regarding the efficacy of pharmacologic doses of vitamin E mandate further study of the dose-response nature of pharmacologic vitamin E therapy from both an efficacy and toxicity perspective.

Animals↗
PubMed1987

A gravimetric technique for evaluating flow continuity from two infusion devices.

A computerized gravimetric technique for examining the flow continuity from infusion devices was developed, and two infusion devices with different mechanisms of pump operation were evaluated to illustrate this technique. A BASIC program that records serial weight measurements and calculates weight change from previous determinations was written for and interfaced with a gravimetric balance and IBM PC. A plot of effused weight (normalized weight change that reflects the difference between desired timed-sample interval and actual time) versus time (desired timed-sample interval) was constructed. The gravimetric technique was evaluated using both a peristaltic-type and a piston-type infusion pump. Intravenous solution (5% dextrose and 0.9% sodium chloride) was effused at 10 mL/hr and collected in a beaker. Weights were measured at 10-second intervals over a two-hour infusion period, and the weights of the effused solution were plotted versus time. Flow continuity differed between the two infusion devices. Actual effused weight decreased to 0.007 g/10 sec during the refill cycle of the piston-type pump; the mean (+/- S.D.) effused weight was 0.029 +/- 0.002 g/10 sec. The desired effusion rate was 0.028 g/10 sec. The peristaltic pump had greater flow continuity, with a mean effusion weight of 0.028 +/- 0.003 g/10 sec. The gravimetric technique described in this report can be used to quantitatively depict the effusion profiles of infusion devices. Further studies are needed to identify the degree of flow continuity that is clinically acceptable for infusion devices.

Infusion Pumps↗
PubMed1986

Preface.

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Journal Article↗
PubMed1986

Repair in E. coli of transforming plasmid DNA damaged by psoralen plus near-ultraviolet irradiation.

Treatment of DNA with psoralen plus near-ultraviolet irradiation gives rise to both monoadducts and cross-links. We have examined the repair of plasmid NTP16 DNA treated in this way in vitro and then used to transform E. coli. Monoadducts are found to be potentially lethal, and can be repaired by uvr-dependent and recA-dependent pathways. The presence of a related resident plasmid in the transformed cells can enhance the survival of the incoming damaged NTP16 DNA. This effect is not recA-dependent, and a similar effect (designated "resident enhanced repair") has been observed previously with UV-irradiated plasmids of this particular incompatibility group. Removal of unbound psoralen from the plasmid DNA and exposure to further NUV is known to increase the ratio of cross-links to monoadducts, and we demonstrate that such cross-linked plasmid DNA is not readily repaired following transformation. However in the presence of homologous DNA (related resident plasmid) there is evidence for the repair, and hence uptake by the cell, of cross-linked DNA.

Calcium↗
PubMed1986

Disposition of intravenously administered pharmacologic doses of vitamin E in newborn rabbits.

Newborn rabbits were given a single intravenous dose (100 mg/kg) of either alpha-tocopherol or alpha-tocopheryl acetate to compare disposition characteristics of these two forms of vitamin E. The resulting tissue concentrations of alpha-tocopherol and alpha-tocopheryl acetate differed significantly. Tissue concentrations of either form of vitamin E were much higher than those provided by normal nutrition, and remained unchanged (except in the liver) for 6 days after dose. alpha-Tocopheryl acetate was not completely converted to alpha-tocopherol, and only 50% of the dose was recovered 3 days after administration. The entire dose of alpha-tocopherol was recovered intact 3 days after administration. The persistence of very high tissue vitamin E concentrations after a single intravenous dosing, the disappearance from the body of half of the administered dose of alpha-tocopheryl acetate, and the lack of complete conversion of alpha-tocopheryl acetate to alpha-tocopherol when given intravenously have profound implications regarding the current clinical practice of giving repeated pharmacologic doses of vitamin E to newborn infants.

Animals↗
PubMed1986

Phenothiazine and butyrophenone intoxication in children.

Antipsychotic agents are widely used for the treatment of psychotic disorders as well as for the acute treatment of nausea and vomiting, cough and cold treatments, and as supplementary agents for sedation for minor surgical or diagnostic procedures. There are many different circumstances in which the clinician may encounter a child who has experienced antipsychotic drug toxicity, such as from an acute accidental ingestion or as a side effect from therapeutic use. The phenothiazines and butyrophenone drugs have many pharmacologic actions. Thus, a wide range of clinical symptoms and signs may be encountered with their use. Treatment of antipsychotic drug toxicity includes general supportive care and monitoring, along with specific treatment of certain situations such as acute extrapyramidal syndromes and neuroleptic malignant syndrome. An awareness of the diverse and complex manifestations that may be associated with these agents will greatly aid in the evaluation of a child who presents with unusual behavioral or neurologic problems. Due to the unpredictable toxicity of these drugs, routine therapeutic use for such conditions as nausea and vomiting and as cough or cold aids is not recommended.

Absorption↗
PubMed1986

The effect of the relationship between punch velocity and particle size on the compaction behaviour of materials with varying deformation mechanisms.

The effect of punch velocity over the range 0.033-300 mm s-1 on the compaction properties of lactose, microcrystalline cellulose and a drug substance (a phthalazine derivative) for a range of particle sizes has been studied using the yield pressure derived from the Heckel relationship and a strain rate sensitivity index (SRS index), as the criteria to describe their behaviour. For lactose, a material which deforms by a mixed mechanism of particle fracture and plastic deformation at the contact points, the yield pressure increased and the SRS index decreased as particle size decreased, due to a reduction in the amount of fragmentation of the particles. For microcrystalline cellulose, a material which is known to deform plastically, the yield pressure and the SRS index were independent of particle size. For the phthalazine derivative the yield pressure increased as particle size decreased; however the SRS index reduced from 41% to zero, indicating that the deformation mechanism was changing from plastic flow to brittle behaviour. This decrease in the SRS index has been explained in terms of the relative amounts of strain-hardened material produced as milling severity increased, resulting in an increasing resistance to deformation and thus an apparent increase in brittle behaviour as particle size decreased.

Cellulose↗
PubMed1986

Brittle fracture propensity measurements on 'tablet-sized' cylindrical compacts.

The brittle fracture propensity test which was originally designed for large, square compacts with a central hole has been modified and extended to compacts of 'tablet-sized' dimensions. This allows a brittle fracture propensity (BFP) index to be measured at strain rates and conditions approaching those normally used in tableting. The BFP indices for microcrystalline cellulose, Tablettose and heavy magnesium carbonate were evaluated at punch velocities of 3.33 and 200 mm s-1 and found to be in good agreement with the results of previous workers.

Hardness↗
PubMed1986

Cloning and characterization of the dcm locus of Escherichia coli K-12.

The dcm locus of Escherichia coli K-12 has been shown to code for a methylase that methylates the second cytosine within the sequence 5'-CC(A/T)GG-3'. This sequence is also recognized by the EcoRII restriction-modification system coded by the E. coli plasmid N3. The methylase within the EcoRII system methylates the same cytosine as the dcm protein. We have isolated, from a library of E. coli K-12 DNA, two overlapping clones that carry the dcm locus. We show that the two clones carry overlapping sequences that are present in a dcm+ strain, but are absent in a delta dcm strain. We also show that the cloned gene codes for a methylase, that it complements mutations in the EcoRII methylase, and that it protects EcoRII recognition sites from cleavage by the EcoRII endonuclease. We found no phage restriction activity associated with the dcm clones.

Base Sequence↗
PubMed1986

Lytic and transforming functions of individual products of the adenovirus E1A gene.

To distinguish the individual roles of the 13S, 12S, and 9S adenovirus E1A gene products, we isolated the corresponding cDNA clones and recombined them into both plasmids and viruses. Only the expected E1A mRNA products were made from the corresponding 12S and 13S viruses. The 9S mRNA was detected when the 9S virus was coinfected with the 13S virus but not when either virus was infected alone. The 13S virus formed plaques equally well in 293 cells, HeLa cells, and A549 cells, a human lung oat cell carcinoma line. Plaque titers of the 12S virus were much reduced in HeLa and A549 cells compared with 293 cells, although the 12S virus is multiplicity-dependent leaky in both HeLa and A549 cells. A549 cells were significantly more permissive than HeLa cells for growth of the 12S virus. In A549 cells even at low multiplicities of infection the final yield of 12S virus eventually approached the maximum yield from 293 cells. Expression from the adenovirus early region 2 and early region 3 promoters in HeLa cells was activated in the presence of a 13S cDNA E1A region but not in the presence of a 12S E1A cDNA region. Although defective for lytic growth in HeLa cells, the 12S virus immortalized BRK cells at very high efficiency, whereas infection of these cells with 13S virus, as with wild-type E1A virus, resulted mainly in cell death. The 13S product does have an immortalization function, however, revealed in the absence of adenovirus lytic functions when a plasmid containing the E1A 13S cDNA region was transfected into BRK cells. The 9S virus failed to immortalize infected BRK cells or to interfere with focus formation when coinfected with the 12S virus.

Adenovirus Early Proteins↗