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Biomedical subjects

A Chambers

Publications and source records attributed to A Chambers.

At least 19 recordsLinked to original sources
PubMed2006

The effect of sodium chloride on the dissolution of calcium silicate hydrate gels.

The use of cement based materials will be widespread in the long-term management of radioactive materials in the United Kingdom. One of the applications could be the Nirex reference vault backfill (NRVB) as an engineered barrier within a deep geological repository. NRVB confers alkaline conditions, which would provide a robust chemical barrier through the control of the solubility of some key radionuclides, enhanced sorption and minimised corrosion of steel containers. An understanding of the dissolution of C-S-H gels in cement under the appropriate conditions (e.g., saline groundwaters) is necessary to demonstrate the expected evolution of the chemistry over time and to provide sufficient cement to buffer the porewater conditions for the required time. A programme of experimental work has been undertaken to investigate C-S-H gel dissolution behaviour in sodium chloride solutions and the effect of calcium/silicon ratio (C/S), temperature and cation type on this behaviour. Reductions in calcium concentration and pH values were observed with samples equilibrated at 45 degrees C compared to those prepared at 25 degrees C. The effect of salt cation type on salt-concentration dependence of the dissolution of C-S-H gels was investigated by the addition of lithium or potassium chloride in place of sodium chloride for gels with a C/S of 1.0 and 1.8. With a C/S of 1.0, similar increases in dissolved calcium concentration with increasing ionic strength were recorded for the different salts. However, at a C/S of 1.8, anomalously high calcium concentrations were observed in the presence of lithium.

Calcium Compounds↗
PubMed2005

The telomere-binding protein Taz1p as a target for modification by a SUMO-1 homologue in fission yeast.

In fission yeast (Schizosaccharomyces pombe) the homologue of the mammalian SUMO-1 ubiquitin-like modifier is encoded by the pmt3 gene. A two-hybrid screen using the telomere-binding protein Taz1p as bait identified Pmt3p as an interacting factor. In vitro experiments using purified components of the fission yeast Pmt3p modification system demonstrated that Taz1p could be modified directly by Pmt3p. The amino acid sequence of Taz1p contains a close match to the consensus modification site for SUMO-1, and a PEST sequence similar to those found in established SUMO-1 targets. Although previous experiments have identified an increase in telomere length as one consequence of the pmt3--genotype, we could not detect Pmt3p modification of Taz1p in protein extracts made from exponentially growing haploid cells or any effect of Pmt3p on the localization of GFP-Taz1p at discrete foci in the haploid cell nucleus.

Repressor Proteins↗
PubMed2004

Therapeutic impact of abdominopelvic computed tomography in patients with acute abdominal symptoms.

PURPOSE: To determine the diagnostic and therapeutic impact of abdominopelvic computed tomography (CT) in patients with acute abdominopelvic pain. MATERIAL AND METHODS: Referring clinicians completed pre-CT and post-CT questionnaires for 50 patients in whom CT had been requested because of acute abdominopelvic pain. Clinicians recorded their leading diagnosis, confidence in this, and intended management. Following CT, clinicians again recorded these responses in the light of CT findings. Responses pre-CT and post-CT were compared in order to determine diagnostic and therapeutic impact. RESULTS: Diagnostic confidence rose significantly following CT (mean score 6.8 pre-CT versus 8.3 post-CT; P<0.0001). Intended management changed because of CT findings in 29 (58%) patients: 14 (28%) subjects whose intended management was surgical were treated medically and an additional 2 were transferred to gynecological care; 4 patients whose intended management was medical were treated surgically; 2 patients whose intended management was medical were treated by percutaneous drainage; a patient whose intended management was percutaneous drainage was treated by surgery. Of 6 patients with uncertain management pre-CT, 2 were treated surgically and 4 medically. The leading diagnosis also changed as a consequence of CT in 7 (33%) of 21 patients in whom intended management did not alter. CONCLUSION: CT in patients with acute abdominopelvic pain has considerable diagnostic and therapeutic impact, altering management in 58% of patients studied. The major effect is to avert intended laparotomy.

Abdomen, Acute↗
PubMed2002

The therapeutic impact of abdominal ultrasound in patients with acute abdominal symptoms.

AIM: The technical performance of abdominal ultrasound in the investigation of acute abdominal pain has been thoroughly investigated but its therapeutic effects are less well understood. We aimed to determine the therapeutic effect of abdominal ultrasound in the investigation of acute abdominal pain. MATERIAL AND METHODS: A pre- and post-intervention observational study design was used to determine the diagnostic and therapeutic effects of abdominal ultrasound for acute abdominal pain. Referring clinicians completed a pre-ultrasound questionnaire that detailed their leading diagnosis, confidence in this and intended management in 100 consecutive adult patients. Following ultrasound a second questionnaire was completed. This again detailed the leading diagnosis, confidence in this and their intended management. Clinicians quantified the management contribution of ultrasound both for the individual case in question and in their clinical experience generally. RESULTS: The leading diagnosis was either confirmed or rejected in 72 patients and a new diagnosis provided where no prior differential diagnosis existed in 10. Diagnostic confidence increased significantly following ultrasound (mean score 6.5 pre-ultrasound vs 7.6 post-ultrasound, P < 0.001). Intended management changed following ultrasound in 22 patients; 15 intended laparotomies were halted and a further seven patients underwent surgery where this was not originally intended. Ultrasound was rated either 'very' or 'moderately' helpful in 87% of patients, with 99% of clinicians finding it either 'very' or 'moderately' helpful generally. CONCLUSION: Abdominal ultrasound has considerable diagnostic and therapeutic effect in the setting of acute abdominal pain.

Abdomen, Acute↗
PubMed2001

The N-terminal and C-terminal domains of RAP1 are dispensable for chromatin opening and GCN4-mediated HIS4 activation in budding yeast.

Repressor activator protein 1 (RAP1) assists GCN4-mediated HIS4 activation by overcoming some repressive aspect of chromatin structure to facilitate GCN4 binding. RAP1 also participates in other nuclear processes, and discrete domains of RAP1 have been shown to have specific properties including DNA binding, DNA bending, transcriptional activation, and silencing and telomere functions. To investigate whether specific domains of RAP1 are required to "open" chromatin and help GCN4 to activate the HIS4 gene, we examined the abilities of different truncated RAP1 proteins to perturb positioned nucleosomes via a nucleosomal RAP1 site in a yeast episome in vivo, and we tested HIS4 activation in yeast strains harboring truncated RAP1 mutants. We found that neither the DNA bending domain nor the putative activation domain of RAP1 is required for its ability to perturb the chromatin structure of a plasmid containing a RAP1 site. Similarly, neither the putative activation domain nor the N-terminal DNA-bending domain was required for GCN4-mediated activation of HIS4. We also used a rap1(ts) mutant to show that continuous occupancy of the HIS4 promoter by RAP1 is required for GCN4-mediated gene activation.

Alcohol Oxidoreductases↗
PubMed2001

Pharmacological differences between the human and rat vanilloid receptor 1 (VR1).

Vanilloid receptors (VR1) were cloned from human and rat dorsal root ganglion libraries and expressed in Xenopus oocytes or Chinese Hamster Ovary (CHO) cells. Both rat and human VR1 formed ligand gated channels that were activated by capsaicin with similar EC(50) values. Capsaicin had a lower potency on both channels, when measured electrophysiologically in oocytes compared to CHO cells (oocytes: rat=1.90+/-0.20 microM; human=1.90+/-0.30 microM: CHO cells: rat=0.20+/-0.06 microM; human=0.19+/-0.08 microM). In CHO cell lines co-expressing either rat or human VR1 and the calcium sensitive, luminescent protein, aequorin, the EC(50) values for capsaicin-induced responses were similar in both cell lines (rat=0.35+/-0.06 microM, human=0.53+/-0.03 microM). The threshold for activation by acidic solutions was lower for human VR1 channels than that for rat VR1 (EC(50) pH 5.49+/-0.04 and pH 5.78+/-0.09, respectively). The threshold for heat activation was identical (42 degrees C) for rat and human VR1. PPAHV was an agonist at rat VR1 (EC(50) between 3 and 10 microM) but was virtually inactive at the human VR1 (EC(50)>10 microM). Capsazepine and ruthenium red were both more potent at blocking the capsaicin response of human VR1 than rat VR1. Capsazepine blocked the human but not the rat VR1 response to low pH. Capsazepine was also more effective at inhibiting the noxious heat response of human than of rat VR1.

Amino Acid Sequence↗
PubMed2000

Sequence-specific binding of Taz1p dimers to fission yeast telomeric DNA.

The fission yeast (Schizosaccharomyces pombe) taz1 gene encodes a telomere-associated protein. It contains a single copy of a Myb-like motif termed the telobox that is also found in the human telomere binding proteins TRF1 and TRF2, and Tbf1p, a protein that binds to sequences found within the sub-telomeric regions of budding yeast (Saccharomyces cerevisiae) chromosomes. Taz1p was synthesised in vitro and shown to bind to a fission yeast telomeric DNA fragment in a sequence specific manner that required the telobox motif. Like the mammalian TRF proteins, Taz1p bound to DNA as a preformed homodimer. The isolated Myb-like domain was also capable of sequence specific DNA binding, although with less specificity than the full-length dimer. Surprisingly, a protein extract produced from a taz1- fission yeast strain still contained the major telomere binding activity (complex I) we have characterised previously, suggesting that there could be other abundant telomere binding proteins in fission yeast. One candidate, SpX, was also synthesised in vitro, but despite the presence of two telobox domains, no sequence specific binding to telomeric DNA was detected.

Amino Acid Sequence↗
PubMed1999

In vivo analysis of functional regions within yeast Rap1p.

We have analyzed the in vivo importance of different regions of Rap1p, a yeast transcriptional regulator and telomere binding protein. A yeast strain (SCR101) containing a regulatable RAP1 gene was used to test functional complementation by a range of Rap1p derivatives. These experiments demonstrated that the C terminus of the protein, containing the putative transcriptional activation domain and the regions involved in silencing and telomere function, is not absolutely essential for cell growth, a result confirmed by sporulation of a diploid strain containing a C terminal deletion derivative of RAP1. Northern analysis with cells that expressed Rap1p lacking the transcriptional activation domain revealed that this region is important for the expression of only a subset of Rap1p-activated genes. The one essential region within Rap1p is the DNA binding domain. We have investigated the possibility that this region has additional functions. It contains two Myb-like subdomains separated by a linker region. Individual point mutations in the linker region had no effect on Rap1p function, although deletion of the region abolished cell growth. The second Myb-like subdomain contains a large unstructured loop of unknown function. Domain swap experiments with combinations of elements from DNA binding domains of Rap1p homologues from different yeasts revealed that major changes can be made to the amino acid composition of this region without affecting Rap1p function.

Amino Acid Sequence↗
PubMed1999

Peritonsillar abscess (PTA) in children.

1. PTA is more common in young adults, but does occur in young children. The average age in this present series was 8 years. 2. Children with progressive sore throat, sometimes despite antibiotics, should cause suspicion of a PTA. Edema and erythema of the affected tonsil with edema of the uvula and displacement toward the opposite side are classically seen. 3. In older or more cooperative children, fine needle aspiration of the affected tonsil allows prompt diagnosis of PTA. 4. Antibiotic therapy should consist of a cephalosporin owing to high tissue concentration within the inflamed peritonsillar tissue. 5. Definitive treatment is a Quinsy tonsillectomy. Immediate tonsillectomy not only drains the abscess, but also eliminates the potential for an occult inferior pole or contralateral abscess. It also spares the child a future hospitalization and surgical procedure.

Adolescent↗
PubMed1996

Rap1p is a negative regulator of the RAP1 gene.

The promoter of the RAP1 gene contains four potential binding sites for Rap1p, located between the UAS and the RNA initiation site. We have confirmed that three of these sites are recognised by Rap1p in vitro. Different combinations of the three sites were then mutated to abolish Rap1p binding, and the effect of these mutations on promoter activity was determined. When all three Rap1p sites were mutated, the activity of the promoter increased by about 130%, indicating that at least one of the sites is a negative element. Analysis of promoters with different combinations of the mutant sites revealed that the 5'-most site (A) is the principal target for repression. To test the involvement of Rap1p in controlling RAP1 expression, we have measured transcription of the chromosomal RAP1 gene in a RAP1 wild-type strain and two strains containing rap1ts mutations. At a semi-permissive temperature, the RAP1 promoter was more active in the rap1ts strains than in the RAP1 wild-type strain, suggesting that expression of the chromosomal RAP1 gene is greater when the activity of Rap1p in the cell is compromised. The activities of the wild-type promoter, and the promoter with mutations in the three Rap1p-binding sites, were compared in sir1, sir2, sir3 and sir4 mutant strains. In each case, the mutated promoter was significantly more active than the wild-type promoter, implying that the repression mechanism is not dependent on any one of the SIR gene products.

Base Sequence↗
PubMed1996

DNA-protein interactions at the telomeric repeats of Schizosaccharomyces pombe.

Gel retardation assays using a probe containing the repeat region of a Schizosaccharomyces pombe chromosomal telomere identified four specific DNA- protein complexes in S. pombe total protein extracts (I, I', IIa and IIb). The proteins responsible for these complexes bound to the telomeric repeat region irrespective of whether or not the repeats were in close proximity to the end of a DNA molecule, and none of them bound strongly to single-stranded DNA. The protein responsible for complex I (TeRF I) was separated from the activity responsible for complexes IIa and IIb (TeRF II) using heparin-Sepharose chromatography. Both factors were efficiently cross-competed by an oligonucleotide containing the 18 bp sequence 5'-GGTTACAGGTTACAGGTT-3', which corresponds to two complete telomeric repeat units. Mutation of the T residues at positions 4 and 11 in the oligonucleotide dramatically reduced binding by TeRF II, but had no affect on binding by TeRF I. The protein responsible for complex I' did not bind strongly to either the wild-type or mutant oligonucleotide.

Base Sequence↗
PubMed1996

The multifunctional transcription factors Abf1p, Rap1p and Reb1p are required for full transcriptional activation of the chromosomal PGK gene in Saccharomyces cerevisiae.

We have identified two new transcription factor binding sites upstream of the previously defined UAS within the phosphoglycerate kinase (PGK) gene promoter in Saccharomyces cerevisiae. These sites are bound in vitro by the multifunctional factors Cpf1p and Reb1p. We have generated targeted deletions of Rap1p, Abf1p and Reb1p binding sites in the promoter of the chromosomal copy of the PGK gene. Northern blot analysis confirmed that most PGK promoter activity is mediated through the Rap1p binding site. However, significant effects are also mediated through both the Reb1p and Abf1p sites. In contrast, when the promoter is present on a high-copy-number plasmid, both the Abf1p and Reb1p sites play no role in transcriptional activation. The role of Cpf1p was examined using a cpf1 null strain. Cpf1p was found to have little if any, effect on activation of either the chromosomal or plasmid-borne PGK gene.

Base Sequence↗
PubMed1996

Highly conserved toxicity of Saccharomyces cerevisiae Rap1p.

Budding yeast (Saccharomyces cerevisiae) Rap1p has been expressed in fission yeast (Schizosaccharomyces pombe) under the control of the regulatable fructose bisphosphatase (fbp) promoter. When the fbp promoter was derepressed, cells containing the complete RAP1 gene failed to show any significant growth, suggesting that Rap1p is toxic. A derivative of Rap1p that has a temperature-sensitive mutation in the DNA-binding domain was not toxic in cells grown at 37 degrees C, a temperature at which DNA binding by rap1p(ts) is severely inhibited. Removal of a short region downstream of the DNA-binding domain, including a region previously shown to be essential for Rap1p toxicity in budding yeast, also abolished the toxic effect. The toxic effect of Rap1p has therefore been conserved between two distantly related yeasts. In budding yeast, overexpression of Rap1p also caused changes to the lengths of the telomeric repeats. No effects on telomeres were detected in fission yeast.

Blotting, Southern↗