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W D Morgan

Publications and source records attributed to W D Morgan.

At least 55 records · Page 3Linked to original sources
PubMed1989

Calibration and evaluation of a 252Cf-based neutron activation analysis instrument for the determination of nitrogen in vivo.

A novel clinical instrument for multi-element in vivo neutron activation analysis has been recently constructed in Swansea. The instrument is intended primarily for prompt gamma measurement of total and partial body calcium, total body nitrogen and partial body cadmium. For the measurement of nitrogen the subject is scanned both prone and supine across a vertical collimated neutron beam from a 4 GBq 252Cf source. Two shielded Nal(TI) detectors, each of volume 2760 cm3, are placed above the subject on the opposite side to that irradiated. The prompt gamma ray spectrum contains prominent peaks from hydrogen, nitrogen, chlorine and carbon. The optimisation, calibration and evaluation of the instrument for the measurement of nitrogen, by the reaction 14N(n, gamma)15N, is described. The calibration corrects the ratio of nitrogen-to-hydrogen counts measured from the subject for background gamma rays and the effects of body habitus. Body hydrogen is use as as internal standard. Repeated measurements of a homogeneous anthropomorphic phantom indicate that the ratio of nitrogen-to-hydrogen counts may be determined by a coefficient of variation of 1.6% for a neutron dose equivalent incident on the phantom of 0.45 mSv (QF = 10). The accuracy of the calibration was assessed by measuring three anthropomorphic phantoms (weight range: 41.4-110 kg) containing simulated skeletons and the major organs of the body. For these phantoms the mean discrepancy of the measured to the known nitrogen content was +4.9%. The simultaneous measurement of chlorine and carbon is discussed.

Activation Analysis↗
PubMed1989

Transcription factor Sp1 binds to and activates a human hsp70 gene promoter.

I investigated the binding of purified transcription factor Sp1 from HeLa cells to the human hsp70 promoter by DNase I footprinting. Three binding sites were detected within the upstream promoter region, including one located 46 base pairs upstream of the transcription start, between the TATA box and the proximal CCAAT box element. In vitro transcription demonstrated that the proximal site is capable of responding to Sp1-dependent stimulation. These results suggest that Sp1 might contribute to constitutive expression in vivo and might also be involved in the various regulatory responses that affect this gene.

Base Sequence↗
PubMed1987

A clinical instrument for multi-element in vivo analysis by prompt, delayed and cyclic neutron activation using 252Cf.

The design and construction of a versatile clinical instrument for multi-element in vivo neutron activation analysis of major and minor body elements is described. A 200 micrograms (4 GBq) 252Cf neutron source is stored below ground level and pneumatically propelled to one of two irradiation ports. These deliver collimated beams of fast neutrons either to a localised volume such as the liver or kidney, or across the width of a patient for a head-to-toe scanning whole-body measurement. The source control system allows selection of either a continuous or cyclic mode of activation. The instrument is intended primarily for measurement, by the prompt-gamma technique, of total and partial body calcium, total body nitrogen and partial body cadmium. The potential of the instrument for determination of these three elements has been established. Phantom results suggest that total body calcium can be measured with a precision of +/- 2.6% (CV) for an average whole-body skin dose equivalent of 6.4 mSv; total body nitrogen with a precision of +/- 2.0% for an average whole-body skin dose equivalent of less than 0.4 mSv; and a detection limit (2 SD of the background) of 2.4 mg of cadmium in the kidney has been obtained for a radiation dose equivalent to the skin of 3 mSv (QF = 10). The suitability of this instrument for the measurement of other elements is also discussed.

Californium↗
PubMed1987

Two transcriptional activators, CCAAT-box-binding transcription factor and heat shock transcription factor, interact with a human hsp70 gene promoter.

We characterized the activity of a human hsp70 gene promoter by in vitro transcription. Analysis of 5' deletion and substitution mutants in HeLa nuclear extracts showed that the basal activity of the promoter depends primarily on a CCAAT-box sequence located at -65. A protein factor, CCAAT-box-binding transcription factor (CTF), was isolated from HeLa nuclear extracts and shown to be responsible for stimulation of transcription in a reconstituted in vitro system. DNase I footprinting revealed that CTF interacts with two CCAAT-box elements located at -65 and -147 of the human hsp70 promoter. An additional binding activity, heat shock transcription factor (HSTF), which interacted with the heat shock element, was also identified in HeLa extract fractions. This demonstrates that the promoter of this human hsp70 gene interacts with at least two positive transcriptional activators, CTF, which is required for CCAAT-box-dependent transcription as in other promoters such as those of globin and herpes simplex virus thymidine kinase genes, and HSTF, which is involved in heat inducibility.

Base Sequence↗
PubMed1986

Unexpected mobilisation of lead during cisplatin chemotherapy.

During an investigation by X-ray fluorescence of platinum uptake in the kidney after chemotherapy with cisplatin, lead was found to have accumulated in the kidney in four subjects. The average kidney lead burden in one case exceeded 800 micrograms/g. Although two of the subjects had been occupationally exposed to lead, the other two had not. The tibia lead burden was also high in the two subjects in whom it was measured. The origins of this mobilised lead and the implications for cisplatin nephrotoxicity are discussed.

Aged↗
PubMed1985

RNA sequence and secondary structure requirements for rho-dependent transcription termination.

The interaction of E. coli termination factor rho with the nascent RNA transcript appears to be a central feature of the rho-dependent transcription termination process. Based on in vitro studies of the rho-dependent termination of the transcript initiated at the PR promoter of bacteriophage lambda, and on earlier studies, Morgan, Bear and von Hippel (J. Biol. Chem. 258, 9565-9574, 1983) proposed a model defining the features of a potential binding site for rho protein on transcripts subject to rho-dependent termination. This model suggested that an effective rho binding site on a nascent RNA transcript should be: (i) greater than 70-80 nucleotide residues in length; (ii) essentially unencumbered with stable secondary structure; (iii) relatively sequence non-specific; and (iv) located within a few hundred nucleotide residues upstream of the potential rho-dependent terminus. In this paper we examine the sequences and secondary structures of several transcripts that exhibit rho-dependent termination to test this hypothesis further. Unstructured regions of approximately the expected size and location were found on all the transcripts examined. Though several short specific sequence elements were found to occur in a very similar arrangement on the lambda PR- and lambda PL-initiated transcripts of lambda phage, no such elements of sequence regularity were found on any of the other rho-dependent transcripts. The results of the sequence comparisons reported here strongly support the generality of the "unstructured binding site" hypothesis for rho-dependent termination.

Base Sequence↗
PubMed1985

Escherichia coli transcription termination factor rho has a two-domain structure in its activated form.

Limited tryptic digestion of Escherichia coli transcription termination factor rho [an RNA-dependent nucleoside triphosphatase (NTPase)] yields predominantly two fragments (f1 and f2) when the protein is bound to both poly(C) and ATP. The apparent molecular masses of the two fragments are 31 kDa for f1 and 15 kDa for f2, adding up to the molecular mass of the intact rho polypeptide chain (46 kDa). Sequence analysis of the amino termini demonstrates that f1 is derived from the amino-terminal portion of rho and that the trypsin cleavage that defines f2 occurs at lysine-283. These results suggest that, in the liganded (activated) form, the native rho protein monomer is organized into two distinct structural domains that are separable by a single proteolytic cleavage. The f1 fragment, purified from NaDodSO4/polyacrylamide gels and renatured, binds poly(C) but the f2 fragment does not; neither regains any ATPase activity. ATP- and polynucleotide-dependent changes in the rate of proteolysis and in the character of the fragments produced suggest that rho undergoes a series of conformational transitions as a consequence of RNA binding, NTP binding and NTP hydrolysis. The rate of loss of rho ATPase activity and of intact rho monomers is slower in the presence of adenosine 5'-[gamma-thio]triphosphate than in the presence of either ATP or ADP, indicating that the hydrolysis of ATP may result in different conformational effects than does the binding of this ligand. These findings are discussed within the context of recent models of rho-dependent transcription termination.

Adenosine Triphosphate↗
PubMed1985

A feasibility study for the in vivo measurement of beryllium by photonuclear activation.

Diagnosis of the beryllium-induced disease, berylliosis, is often difficult and always requires that the presence of the metal in tissue be demonstrated. The feasibility of developing an in vivo method of measurement, which exploits the uniquely low photonuclear reaction threshold of 1.67 MeV in beryllium, has been investigated. Suitable photon sources and detector systems were assessed, both experimentally by phantom studies and theoretically by use of a Monte-Carlo neutron transport code. It is concluded that by using a filtered source of 124Sb for bilateral irradiation of the chest, and an array of twenty BF3 counters, beryllium could be measured to an accuracy of 0.33 mg per lung, which corresponds to a 2 SD detection limit of 0.67 mg, for a skin dose of 50 mGy delivered within a period of 90s. Such a facility would be capable of contributing to the aetiology of the disease in a large proportion of cases, but the wider use of the method for screening exposed workers would require further improvements in detection efficiency.

Beryllium↗
PubMed1984

Specificity of release by Escherichia coli transcription termination factor rho of nascent mRNA transcripts initiated at the lambda PR.

We have studied the specificity and kinetics of release of nascent RNA from ternary transcription complexes by Escherichia coli transcription termination factor rho in vitro. Stable ternary complexes, initiated at the lambda PR promoter, were prepared either by quenching the elongation reaction with EDTA or by preventing further elongation by incorporating 3'-O-methyl nucleotides at the 3' end of the nascent RNA chains. We find that rho protein can only release lambda PR-initiated transcripts from ternary complexes in which transcription has proceeded beyond 288 base pairs from PR; shorter chains are not released. Substitution of inosine for guanosine in the nascent RNA permits the rho-dependent release process to operate on complexes located as close as 108-116 base pairs downstream from PR. The regions of the template from which rho can release transcripts correspond, for both guanosine- and inosine-containing RNA, to those within which rho-dependent termination has also been shown to occur (Morgan, W. D., Bear, D. G., and von Hippel, P. H. (1983) J. Biol. Chem. 258, 9553-9564, 9565-9574). The half-time for the major part of the release process is less than 10 s. These results are in good accord with the hypothesis that the specificity of rho-dependent termination is jointly determined by two separable processes: (i) the specificity of rho binding to the nascent RNA chain and (ii) the location and strength of RNA polymerase-pausing sites.

Base Sequence↗
PubMed1983

Rho-dependent termination of transcription. I. Identification and characterization of termination sites for transcription from the bacteriophage lambda PR promoter.

We have conducted a detailed investigation of in vitro transcription from the bacteriophage lambda PR promoter in order to examine various aspects of the mechanism of rho-dependent termination. In these studies, we have focused particularly on nucleotide sequence specificity, both at the termini and at potential rho-binding sites on the mRNA, and on the relationships between elongation, pausing, and termination. Rho-terminated transcripts from restriction fragment templates have been analyzed by polyacrylamide gel electrophoresis, and termination efficiencies have been established by densitometry of autoradiographs. Termination sites on the template have been located by comparing the electrophoretic mobilities of terminated transcripts with those of transcripts of known length that have been artificially terminated by the incorporation of 3'-O-methyl nucleotides. We have identified five discrete rho-dependent termination sites located between 290 and 450 base pairs downstream from the lambda PR promoter. These rho-dependent 3'-termini are somewhat heterogeneous in details of sequence and potential RNA secondary structure, but all possess features that appear to be characteristic of RNA polymerase elongation pausing sites (Morgan, W. D., Bear, D. G., and von Hippel, P. H. (1983) J. Biol. Chem. 258, 9565-9574). The efficiency of termination at individual sites ranges from 20 to 70% under the usual in vitro transcription conditions; termination is inhibited by increasing the monovalent salt concentration. Lowering nucleoside triphosphate substrate concentrations increases termination efficiency at some sites located 290 or more base pairs downstream from PR, but does not enhance termination at sites closer to PR. The substitution of inosine for guanosine residues in the transcript, which decreases the stability of the RNA-DNA hybrid and of secondary structure in the nascent mRNA, results in strong rho-dependent termination at several new sites located 100 to 260 base pairs downstream from PR. In Morgan et al. (cited above), data on RNA polymerase elongation pausing as a function of reaction conditions are correlated with these termination results, and a general model for rho-dependent termination is discussed.

Bacteriophage lambda↗
PubMed1983

Rho-dependent termination of transcription. II. Kinetics of mRNA elongation during transcription from the bacteriophage lambda PR promoter.

The kinetics of elongation of the mRNA that initiates from the lambda PR promoter has been examined using specific restriction fragments as template, and the locations at which significant pausing of the RNA polymerase occurs during in vitro transcription have been established. Major pausing of polymerase, in the absence of rho, occurs at the five rho-dependent termination sites (located between 290 and 450 base pairs downstream from PR) that are described in the accompanying article (Morgan, W. D., Bear, D. G., and von Hippel, P. H. (1983) J. Biol. Chem. 258, 9553-9564). The replacement of guanosine by inosine triphosphate in the transcription mix results in the appearance of new pausing sites; these pausing sites correspond, in part, to the new rho-dependent termini between 100 and 260 base pairs from PR identified in the preceding article (cited above) when inosine replaces guanosine in the transcript. The effects of variations in nucleoside triphosphate and salt concentrations on pausing have also been determined. Analysis of the base pair sequences of pausing sites shows that pausing may result from the presence of dyad symmetry, GC-rich sequences, or (for inosine-substituted transcripts) C-rich sequences in the RNA-DNA hybrid region. Quantitation of RNA polymerase pausing at termination loci indicates that pausing sites with relaxation times of 10 to 25 s (at 37 degrees C and 100 to 200 mM KCl) can lead to significant rho-dependent termination. In addition, increasing the length of "natural" pauses by lowering the concentrations of specific nucleoside triphosphate substrates can lead to increased termination efficiency, but only at sites that correspond to rho-dependent termini in elongation experiments conducted at standard concentrations of nucleoside triphosphates. These results, and the findings of the article cited above, are interpreted in terms of a two-component model for rho-dependent termination. Required are: (i) a significant pause in transcript elongation due to sequence and/or structural features at the termination site(s); and (ii) a rho-binding site(s) on the nascent mRNA that is long (70-90 nucleotide residues) and relatively free of secondary structure, and that contains appropriate sequences of cytidine residues.

Bacteriophage lambda↗
PubMed1983

Isozyme phenotypes of polyoma virus tumors in mice.

Isozyme profiles for 32 enzyme systems were studied in tumors induced by two strains of polyoma virus (2PTA and LID1), in two conventional mouse strains (C3H/BiDa and NIH), and in athymic (nude) mice of two genetic backgrounds (C3H/Hes nu/nu and NIH nu/nu). Tumors studied were: primary and transplant passages of salivary gland tumors (127); primary thymic epithelial tumors (12); primary subcutaneous sarcomas (6); primary hair follicle tumors (5); primary and transplant passages of mammary tumors (18); primary ameloblastomas (3); and primary renal medullary sarcomas (3). Regardless of mouse strain or virus strain, the isozyme arrays were highly constant and unique for each tumor histotype with the exception of salivary and mammary tumors, which shared a single profile differing from that of each of the other histotype-associated profiles. Other tumor types could be distinguished from each other and from the salivary-mammary tumor pair by as few as five isozymes: glycerol-3-phosphate dehydrogenase; glyceraldehydephosphate dehydrogenase; lactate dehydrogenase; sorbitol dehydrogenase; and alkaline phosphatase. Twelve nonpolyoma mammary tumors and their passages from mouse mammary tumor virus-expressed C3H/Hes nu/+ mice were analyzed for the same enzymes; variations in activity and isozyme profiles were found for ten enzyme systems. Three spontaneous salivary myoepitheliomas in BALB/c mice were also analyzed; two different lactate dehydrogenase profiles were observed, and all three tumors lacked the placental alkaline phosphatase present in polyoma virus-induced salivary tumors. Uniformity of isozyme phenotype may be characteristic of DNA virus transformation of cells in a particular differentiative state. This uniformity does not appear to occur in mouse mammary tumor virus-associated tumors, spontaneous tumors, and, according to the literature, chemically induced tumors.

Alkaline Phosphatase↗
PubMed1981

Critical concentrations of cadmium in human renal cortex: dose-effect studies in cadmium smelter workers.

Cadmium was measured in vivo in the left kidney and liver of 82 industrially exposed workers and 10 control subjects. The range of Cd values for the industrial group was 0.9-57 mg for the whole kidney and 0.8-120 ppm for the liver, compared to 0.4-11.8 mg and 0.6-7.9 ppm for the control group. Below 40 ppm in the liver, the kidney Cd burden tended to increase with increasing liver concentration. Above 40 ppm, the kidney Cd content decreased as the liver concentration increased. This biphasic relation between Cd in the kidney and the liver for all subjects showed a critical level of approximately 31 mg Cd in the kidney. Estimates of the critical level by beta 2-microglobulin and urinary protein measurements yielded critical values of 31-42 mg Cd for the whole kidney (300-400 microgram/g for the renal cortex).

Cadmium↗
PubMed1981

A comparison of 252Cf and 238Pu, Be neutron sources for partial-body in vivo activation analysis.

A comparison is made of the isotopic neutron sources 252 Cf and 238 Pu, Be for partial-body in vivo neutron activation analysis. Depth distributions of thermal neutron fluences in a water phantom are very similar for the two sources. The peak depth occurs at 5 cm. This value is approximately 2 cm less than the values obtained with uncollimated neutrons produced in broad-beam irradiations. With respect to the fluence-to-dose ratio, the 252 Cf neutrons have an advantage of approximately 1.4 over the 238 Pu, Be source. The use of 252 Cf offers two additional advantages for the investigator. First, it minimizes the on-line fast-neutron damage in Ge(Li) semiconductor detectors. Secondly, it is subject to much less stringent transport regulations that 238 Pu, Be. The latter feature takes on particular importance in view of the increasing usefulness of transportable instruments for in vivo cadmium measurements at the workplace.

Beryllium↗
PubMed1981

Calibration of a 238Pu,Be facility for partial-body measurements of organ cadmium.

An improved instrument is described for the measurement of liver and kidney cadmium by in vivo neutron activation analysis in both occupationally and environmentally exposed persons. Detailed calibrations of the instrument used in a study of 83 male workers at a cadmium production plant are give. The importance of accurate organ localisation by ultrasound is stressed, without which errors of 40 and 25% in individual and group kidney measurements, respectively, can occur. The detection limit (2 SD of the background) is 2.2 mg cadmium in the kidney and 1.5 micrograms g-1 (wet weight) in the liver for a local dose of 4.7 mSv. This instrument therefore combines the advantages of portability with high sensitivity of detection of cadmium.

Cadmium↗
PubMed1981

Renal cadmium overload without nephrotoxicity.

A redundant nickel/cadmium battery worker was investigated for non-specific fatigue after completing five years in the industry. Sensitive techniques for in-vivo organ cadmium measurement showed a moderate accumulation in the liver but a very large concentration in the kidneys. Despite this, overall glomerular and tubular function were not impaired. It was concluded that the mechanism of proteinuria observed in some cadmium workers is obscure and not clearly related to the degree of kidney saturation with cadmium.

Adult↗
PubMed1981

Improvement in renal function in primary hyperparathyroidism following parathyroidectomy.

Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured pre- and post-parathyroidectomy in 9 patients with primary hyperparathyroidism. Radiological studies had shown no sign of renal calculi or nephrocalcinosis in these patients. Before operation, GFR ranged from 98.5 to 23.4 ml/min/1.7 m2 and ERPF ranged from 510 to 127 ml/min/1.7 m2. After operation, GFR rose to a range of 108.8 to 48.7 ml/min/1.7 m2, and ERPF ranged from 556 to 189 ml/min/1.7 m2. The results suggest that early diagnosis and surgery are important, both to prevent progressive renal damage and to improve the possibility of recovery where functional damage has occurred.

Adolescent↗