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Biomedical subjects

D Thomas

Publications and source records attributed to D Thomas.

At least 433 records · Page 24Linked to original sources
PubMed1994

Formamidopyrimidine DNA glycosylase in the yeast Saccharomyces cerevisiae.

A DNA glycosylase that excises, 2,6-diamino-4-hydroxy-5N-methylformamidopyrimidine (Fapy) from double stranded DNA has been purified 28,570-fold from the yeast Saccharomyces cerevisiae. Gel filtration chromatography shows that yeast Fapy DNA glycosylase has a molecular weight of about 40 kDa. The Fapy DNA glycosylase is active in the presence of EDTA, but is completely inhibited by 0.2 M KCl. Yeast Fapy DNA glycosylase does not excise N7-methylguanine, N3-methyladenine or uracil. A repair enzyme for 7,8-dihydro-8-oxoguanine (8-OxoG) co-purifies with the Fapy DNA glycosylase. This repair activity causes strand cleavage at the site of 8-OxoG in DNA duplexes. The highest rate of incision of the 8-OxoG-containing strand was observed for duplexes where 8-OxoG was opposite guanine. The mode of incision at 8-OxoG was not established yet. The results however suggest that the Fapy- and 8-OxoG-repair activities are associated with a single protein.

Base Sequence↗
PubMed1994

The vacuolar compartment is required for sulfur amino acid homeostasis in Saccharomyces cerevisiae.

In order to isolate new mutations impairing transcriptional regulation of sulfur metabolism in Saccharomyces cerevisiae, we used a potent genetic screen based on a gene fusion expressing XylE (from Pseudomonas putida) under the control of the promoter region of MET25. This selection yielded strains mutated in various different genes. We describe in this paper the properties of one of them, MET27. Mutation or disruption of MET27 leads to a methionine requirement and affects S-adenosylmethionine (AdoMet)-mediated transcriptional control of genes involved in sulfur metabolism. The cloning and sequencing of MET27 showed that it is identical to VPS33. Disruptions or mutations of gene VPS33 are well known to impair the biogenesis and inheritance of the vacuolar compartment. However, the methionine requirement of vps33 mutants has not been reported previously. We show here, moreover, that other vps mutants of class C (no apparent vacuoles) also require methionine for growth. Northern blotting experiments revealed that the met27-1 mutation delayed derepression of the transcription of genes involved in sulfur metabolism. By contrast, this delay was not observed in a met27 disrupted strain. Physiological and morphological analyses of met27-1 and met27 disrupted strains showed that these results could be explained by alterations in the ability of the vacuole to transport or store AdoMet, the physiological effector of the transcriptional regulation of sulfur metabolism.

Amino Acids, Sulfur↗
PubMed1994

Detection of terminal transferase in acute myeloid leukemia by flow cytometry.

The purpose of this study was twofold: (1) to develop an optimized, reliable method for the flow cytometric analysis of the intranuclear DNA polymerase, terminal deoxynucleotidyl transferase (TdT) in acute myeloid leukemia, and (2) to establish the usefulness of a novel, fluorescein-isothiocyanate conjugated monoclonal anti-TdT antibody (HT-6) in double-fluorescence staining for surface antigens in the characterization of leukemic cells. Inclusion of an aldehyde blocking buffer in the staining protocol reduced background fluorescence sufficiently to allow for the detection of the low-level fluorescent TdT+ myeloblasts. When admixed to normal peripheral blood mononuclear cells, 0.4-0.5% of HLA-DR+ or myeloid surface antigen+, TdT+ double-stained myeloblasts could be reliably detected above background levels. Flow cytometric TdT measurements using the HT-6 antibody in 55 patients with TdT+ acute lymphocytic or myelocytic leukemia or blast crisis of chronic myelogenous leukemia were equal or superior to the results obtained with a mixture of monoclonal anti-TdT antibodies (anti-HTDT-Mix) and comparable to those obtained by the conventional slide method employing polyclonal rabbit anti-human TdT antiserum. This flow cytometric TdT determination in combination with surface antigen staining using a novel anti-TdT monoclonal antibody (HT-6) allows for the recognition of minimal leukemic blast cells during clinical remission in acute myeloid leukemia.

Acute Disease↗
PubMed1994

The provision of oral surgery services in England and Wales 1984-1991.

Data from the Department of Health and the Dental Practice Board demonstrate substantial increases in the volume of oral surgery performed in England and Wales both in the General Dental and Hospital Services during the period 1984-1991. In the General Dental Service, although the number of routine extractions decreased by 10%, the number of surgical procedures increased by 20%, with a substantial increase (33%) in the number of third molar extractions in the period 1988-1991. There have been no decreases in the annual rate of extractions of permanent and deciduous teeth in the GDS since 1987. In at least one Regional Health Authority, there was a five-fold increase in the number of oral surgery patients aged 0-9 years treated in the hospital service (1982-1991). Overall, although this study takes no account of extractions carried out in the Community Service, these findings suggest that numbers of deciduous extractions may have actually risen in some areas, particularly after 1987. In the Hospital Service there was a 55% increase in numbers of day-cases, from 30,090 (1984) to 46,499 (1990); a 10% increase in throughput of in-patients and a 13% decrease in numbers of people waiting for in-patient surgery. These changes were in the same direction as those in plastic and ENT surgery; though plastic surgery achieved a greater utilisation of day-care services. The implications of these changes and their possible effect on the future provision of oral and maxillofacial surgery services are discussed.

Apicoectomy↗
PubMed1994

Isolation, characterization and structure of bacterial flagellar motors containing the switch complex.

A putative complex of the three switch proteins, FliG, FliM and FliN appears to be directly involved in torque generation and control of direction of rotation. We have developed a preparative procedure for flagellar motors that retains these proteins as evidenced by Western blots using anti-FliG, anti-FliM and anti-FliN antibodies. Immunogold labeling with these three antibodies shows that the three switch proteins are localized to the motor. Electron micrographs of frozen-hydrated preparations reveal a large, new component we have termed the "C ring complex" attached to the cytoplasmic face of the M ring. In a three-dimensional reconstruction of the cylindrically averaged structure, the M-S ring complex appears thicker and wider by the addition of extra material to the cytoplasmic surface of the M ring. In addition, extending into the cytoplasm from the thickened M ring is the C ring complex, a thin-walled cylinder having a length of 170 A and an outer diameter of 450 A compared to the 290 A diameter of the M ring. We provide evidence that the thickened M ring contains FliG and that the C ring complex may contain FliM and FliN. The large diameter of the C ring complex may permit interaction with the M ring and with the circlet of studs thought to be the MotA/MotB complex.

Bacterial Proteins↗
PubMed1994

Fullerene-like organization of HIV gag-protein shell in virus-like particles produced by recombinant baculovirus.

Virus-like particles produced by a recombinant baculovirus containing the HIV gag gene were examined by negative staining after delipidization. This technique demonstrated that the gag-protein shell consisted of radially arranged short rods which formed a network of ring-like structures. Similar structures were observed at the plasma membrane of infected cells which had been opened by wet-cleaving. Occasionally five or six subunits were observed forming a ring. These findings suggest that the gag-encoded precursor (pr55) is a rod-like molecule about 34 A in diameter and 85 A in length. A protein cylinder of such dimensions would have a molecular weight of 56K. The center-to-center distance of two neighboring rings formed by the rods was 66 +/- 8 A (N = 200) by direct measurements and 65 A as obtained from averaged images. This morphology and these dimensions indicate that the virus-like particles contain the gag precursor in the form of a near-spherical "fullerene-like" icosahedral shell. Our data indicate that the triangulation number of the rings equals 63. However, since one rod of pr55 is shared by two rings, the number of copies of the precursor will be 1890 as opposed to 2522 if the molecules were closely packed. The particle diameter of 102 nm deduced from the proposed model was close to the diameter obtained from thin sections of low-temperature-embedded specimens (103-108 nm).

Animals↗
PubMed1994

Truncated presequences of mitochondrial F1-ATPase beta subunit from Nicotiana plumbaginifolia transport CAT and GUS proteins into mitochondria of transgenic tobacco.

The mitochondrial F1-ATPase beta subunit (ATPase-beta) of Nicotiana plumbaginifolia is nucleus-encoded as a precursor containing an NH2-terminal extension. By sequencing the mature N. tabacum ATPase-beta, we determined the length of the presequence, viz. 54 residues. To define the essential regions of this presequence, we produced a series of 3' deletions in the sequence coding for the 90 NH2-terminal residues of ATPase-beta. The truncated sequences were fused with the chloramphenicol acetyl transferase (cat) and beta-glucuronidase (gus) genes and introduced into tobacco plants. From the observed distribution of CAT and GUS activity in the plant cells, we conclude that the first 23 amino-acid residues of ATPase-beta remain capable of specifically targeting reporter proteins into mitochondria. Immunodetection in transgenic plants and in vitro import experiments with various CAT fusion proteins show that the precursors are processed at the expected cleavage site but also at a cryptic site located in the linker region between the presequence and the first methionine of native CAT.

Amino Acid Sequence↗
PubMed1994

A comparison of four PTSD measures' convergent validities in Vietnam veterans.

We compared the convergent validities of four commonly used post-traumatic stress disorder (PTSD) measures in 80 help-seeking Vietnam veterans by contrasting their intercorrelations. When scored as continuous severity or frequency measures, the Mississippi Scale for Combat-related PTSD's and the Post-Traumatic Stress Disorder Interview's (PTSD-I's) concordances with other measures were similar to one anothers' and generally larger than those of either the Diagnostic Interview Schedule (DIS) PTSD module or the MMPI PTSD scale. However, when used only to identify stress disorder's presence or absence, the four techniques' concordances were nearly identical. This suggested that the four measures have similar convergent validities when used simply to identify PTSD, but that the PTSD-I and Mississippi scale offer better convergent validity than the MMPI or DIS instruments when used as severity measures.

Adult↗
PubMed1994

Eicosanoid biosynthesis in patients with stable angina: beneficial effects of very low dose aspirin.

OBJECTIVE: We assessed the production of eicosanoids and the effects of very low dose aspirin in patients with stable angina under basal conditions and during rapid atrial pacing. BACKGROUND: Platelet activation occurs in acute ischemic syndromes but is still controversial in stable angina. Very low dose aspirin is known to be platelet selective and can be used to test the hypothesis of the platelet origin of increased thromboxane production in stable angina. METHODS: Urinary excretion of eicosanoids was measured in 42 patients, including 24 patients with and 18 patients without coronary artery disease. The effects of 50 mg/day of aspirin were measured at rest and during pacing-induced ischemia in 10 patients with stable angina and were compared with a similar group of patients not treated by aspirin. RESULTS: Excretion of 11-dehydro-thromboxane B2 was 2.6 times higher in patients with stable angina than in healthy subjects (mean [+/- SEM] 74.8 +/- 13.0 [24 patients] vs. 29.0 +/- 5.4 [18 patients] ng/mmol of creatinine, p < 0.01). Urinary prostacyclin metabolite levels did not differ between the two groups. Treatment for 8 days with 50 mg/day of aspirin inhibited platelet cyclooxygenase, as reflected by the 97% reduction of in vitro serum thromboxane production. This aspirin regimen normalized the level of urinary thromboxane metabolites in patients with angina (17.3 +/- 3.4 ng/mmol of creatinine [10 patients], p < 0.001 from baseline level before treatment) and did not change prostacyclin metabolite levels. Atrial pacing in patients with angina not treated with aspirin caused lactate and thromboxane release into the coronary sinus. In patients with very low dose aspirin therapy, pacing did not cause thromboxane release despite inducing myocardial ischemia. However, fractional lactate extraction decreased less sharply in patients with than without aspirin therapy. CONCLUSIONS: Thromboxane production is greatly increased in patients with stable angina. Very low dose aspirin administered to these patients reduces thromboxane synthesis to normal levels, preserves prostacyclin biosynthesis and prevents acute thromboxane release into the coronary circulation during pacing-induced ischemia. Our data suggest that platelets (not monocytes/macrophages) are activated in stable angina to produce thromboxane.

6-Ketoprostaglandin F1 alpha↗
PubMed1994

[A comparative study of the "Levame" type extension splint and the "Low Profile" type extension splint: impact on therapeutic indications].

The most widely used dynamic extension systems, both to straighten the digital flexion retractions as well as to ensure directed mobilization after surgical repair of extensor tendons, are the so-called "Levame" and "Low Profile" splints. This study analysed the application of forces for these two types of extension splints, the directional constraints which they impose and freedom of joint movement which they allow in order to more clearly define the type of motorization to be used as a function of the most frequent indications.

Equipment Design↗
PubMed1994

Differential expression of an endogenous mannose-binding protein R1 during muscle development and regeneration delineating its role in myoblast fusion.

The role of the endogenous brain carbohydrate-binding protein R1 in muscle cell development and regeneration was analysed both in vivo and in vitro. In vivo, R1 was developmentally regulated, with an embryonic 65,00 subunit and a neonatal 67,000 subunit, being replaced progressively by a 135,000 adult form. Lectin R1 was intracellularly localized at birth and in the prenatal period. During development and at the time of myoblast fusion, the antigen was progressively found at the surface, where it remained at low levels in the adult. In vitro, in pure myoblast cultures, only the embryonic form was present. The ultrastructural studies indicated that the lectin could participate in the membrane fusion process during myoblast fusion. The specific role in myoblast fusion, derived from the ultrastructural localization of R1, was evidenced by a strong inhibitory effect of anti-R1 Fab fragments (10-100 micrograms/ml), relative to control Fab fragments. In vivo, the embryonic subunit pattern and subcellular distribution of R1 reappeared in muscle cells after lesion of the adult muscle. This suggested that, as observed in vitro, R1 participated in vivo in the phenomenon of myoblast fusion. Similar modifications in subunit expression were observed in muscles after denervation (the embryonic form of lectin R1 reappearing after lesion), suggesting that R1 could be involved in the process of neuromuscular junction formation. Thus, it is proposed that the carbohydrate-binding protein R1 is an important recognition molecule for the formation of myotubes. Its potential involvement in a recognition process between axons and muscle cells during neuromuscular junction formation is discussed.

Animals↗
PubMed1994

Venous thrombogenesis.

Venous thrombosis develops when stasis in the deep veins of the legs occurs at times of increased coagulability of the blood. This combination leads to the local generation of thrombin, which is the crucial event in the pathogenesis of this disease. Impaired fibrinolysis allows a small platelet-fibrin nidus to grow into an occluding thrombus. Demonstrable damage to the vessel wall does not appear to play a major role in the development of most cases of venous thrombosis. While the biochemical definition of hypercoagulability remains elusive, immunoregulatory cytokines have been shown to impair the normal non-thrombogenicity of the endothelial wall. This leads to local expression of procoagulant activity and resultant fibrin deposition. In the presence of stasis, the stage is then set for the development of clinically significant thrombi. Although hereditary absence of natural anticoagulants has been found in many patients with venous thrombosis, most patients have no detectable abnormality of their blood.

Animals↗
PubMed1994

Pregnancy and prosthetic heart valves: a French cooperative retrospective study of 155 cases.

A French cooperative retrospective study analysed 155 pregnancies in 103 women with prosthetic heart valves: 95 mechanical prosthesis (MP) and 60 bioprostheses (BP). Among them 13 MP and 10 BP were bivalvular and four were mixed implants. In all, 182 (108 MP and 74 BP) prostheses were exposed to the risk of pregnancy. Among the 108 MP-bearing patients, 16 thromboembolic accidents (TEA) were recorded: 10 thromboses in 13 mitral, two aortic and one pulmonary MP. TEA were four times more frequent under oral anticoagulant therapy. Among the 74 BP, seven suffered premature valve failure. Ninety-nine infants were born to 50 MP-bearing women (53%) and 48 BP-bearing patients (80%) (P < 0.001). Twenty miscarriages were reported; they occurred more often under anticoagulant treatment (17%) than without it (4%) P < 0.02). Coumarin-induced embryopathies were rare (only one definitively identified). Because pregnancy with an MP under anticoagulant therapy is dangerous for the mother and may effect the fetus, the therapeutic indications for women of child-bearing age must be taken into consideration. In a women already with an MP at the time of conception, the duration of heparin therapy should be limited to the following two periods: from the 6th to the 12th week (coumarin-induced embryopathies) and during the last 2 weeks of gestation (haemorrhages during delivery and the neonatal period).

Adult↗
PubMed1994

Temporal modifiers of the radon-smoking interaction.

Data on lung cancer mortality in a cohort of 3,347 Colorado Plateau uranium miners was reanalyzed to investigate the role of time-related modifiers of the radon-smoking interaction. A nested case-control sample of the cohort was drawn, matching each of the 258 lung cancer deaths with 15 controls drawn at random from the subjects who were born in the same year and still alive at the time the case died. As reported earlier, the dose response was sublinear for both total radon and total smoking, and their joint effect was approximately multiplicative. We fitted linear multiplicative models to these data, transforming the radon and smoking variables to improve their fit, and then added variables testing various temporal modifying effects and interactions. The strongest modifiers of the main effects of each variable taken separately were latency and duration of exposure. The strongest modifier of the interaction effect was the timing of radon and smoking exposures: Exposure to radon followed by smoking produced a significantly more-than-multiplicative effect, whereas the reverse sequence produced a significantly less-than-multiplicative effect. These findings suggest that smoking may act as a promoter of radon-initiated cells.

Air Pollutants, Radioactive↗