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S D Bell

Publications and source records attributed to S D Bell.

At least 37 records · Page 2Linked to original sources
PubMed1998

RNA molecules that bind to and inhibit the active site of a tyrosine phosphatase.

Protein tyrosine phosphatases (PTPases) are essential proteins in many cellular processes. In vitro selection was used to evolve high affinity RNA aptamers to the Yersinia PTPase from two random pools varying in length. Selected aptamers from the two different pools share a 21-residue conserved sequence. They bind to their target with dissociation constants of 18 and 28 nM and inhibit the enzyme with IC50 values of 10 and 35 nM, but do not bind a related PTPase. Modification of the PTPase's active site cysteine with the alkylating agent iodoacetate results in a loss of binding affinity. These experiments suggest that the selected aptamers act by binding at or near the active site and might therefore be useful in defining the interactions between PTPases and their targets.

Base Sequence↗
PubMed1998

Transcription and translation in Archaea: a mosaic of eukaryal and bacterial features.

The principal components involved in the processes of transcription and translation in Archaea have been identified by a combination of biochemistry and genome sequencing. In many cases, these factors are closely related to previously characterized proteins from Eukarya and Bacteria. Elucidating the function of these proteins will shed considerable light on the evolution of gene regulatory processes.

Archaea↗
PubMed1997

Factor requirements for transcription in the Archaeon Sulfolobus shibatae.

Archaea (archaebacteria) constitute a domain of life that is distinct from Bacteria (eubacteria) and Eucarya (eukaryotes). Although archaeal cells share many morphological features with eubacteria, their transcriptional apparatus is more akin to eukaryotic RNA polymerases I, II and III than it is to eubacterial transcription systems. Thus, in addition to possessing a 10 subunit RNA polymerase and a homologue of the TATA-binding protein (TBP), Archaea possess a polypeptide termed TFB that is homologous to eukaryotic TFIIB. Here, we investigate the factor requirements for transcription of several promoters of the archaeon Sulfolobus shibatae and its associated virus SSV. Through in vitro transcription and immunodepletion, we demonstrate that S. shibatae TBP, TFB and RNA polymerase are not complexed tightly with one another and that each is required for efficient transcription of all promoters tested. Furthermore, full transcription is restored by supplementing respective depleted extracts with recombinant TBP or TFB, indicating that TBP-associated factors or TFB-associated factors are not required. Indeed, gel-filtration suggests that Sulfolobus TBP and TFB are not associated stably with other proteins. Finally, all promoters analysed are transcribed accurately and efficiently in an in vitro system comprising recombinant TBP and TFB, together with essentially homogeneous preparation of RNA polymerase. Transcription in Archaea is therefore fundamentally homologous to that in eukaryotes, although factor requirements appear to be much less complex.

Archaeal Proteins↗
PubMed1996

In vitro selection of aptamers: the dearth of pure reason.

In vitro selection experiments are now routinely used to identify functional nucleic acid residues and structures, and have become a tool for studying molecular recognition, molecular biology, and molecular evolution. Technical innovations that have been made during the past year include the use of modified monomers to increase stability and photocross-linking reagents to improve affinity. These advances should dramatically increase the utility of aptamers in the future.

Consensus Sequence↗
PubMed1995

Trypanosome nuclear factors which bind to internal promoter elements of tRNA genes.

Expression of eukaryotic nuclear encoded tRNA genes requires two transcription factors, TFIIIB and TFIIIC. To determine if the highly evolutionarily diverged parasitic protozoan Trypanosoma brucei possesses any analogous factors, trypanosome nuclear extracts were prepared. Using these extracts in gel-retardation assays on trypanosome tRNA genes we detected three specific protein-DNA complexes, a highly retarded species and a less retarded pair of complexes. Introduction of mutations into the B box of a lysyl tRNA gene greatly reduced formation of all three complexes. Footprinting studies indicated that all complexes protected the B box of the tRNA gene from cleavage. The most highly retarded complex protected both the A and B boxes from DNasel cleavage. The less retarded pair of complexes showed footprints on the B box alone and the lowest B box specific complex is shown to be resistant to the polyanion heparin. All three complexes are demonstrated to induce bends in the DNA on binding.

Animals↗
PubMed1995

Arteriovenous malformation in the pregnant patient: a case study.

Subarachnoid hemorrhage (SAH) due to ruptured arteriovenous malformation (AVM) or aneurysm accounts for 4.4% of all maternal deaths. It is the third most common nonobstetric cause of maternal death. Significant differences, such as timing of the initial bleed and rebleeding, exist between aneurysmal and AVM related SAH. Increased risk of AVM related SAH appears to correlate with the augmented cardiac output of pregnancy, as well as with other coagulation, hemodynamic and endocrinological changes. These changes usually occur between 20 weeks gestation and 6 weeks postpartum. All suspicious neurological signs and symptoms in the gravid patient should be thoroughly evaluated. Although the nursing care of the pregnant patient with an AVM is similar to that of nonpregnant patients, there are specific clinical observations that are relevant to these patients.

Adolescent↗
PubMed1995

Percutaneous gastrostomy and gastrojejunostomy: additional experience in 519 procedures.

PURPOSE: To assess the efficacy and safety of radiologically guided percutaneous placement of gastrostomy and gastrojejunostomy catheters. MATERIALS AND METHODS: Over 6 years, 562 referred patients were considered for gastrojejunostomy or gastrostomy procedures. In 43 cases (7.7%), the procedure was not performed because of overlying viscera, high position of the stomach, or massive ascites. In 478 patients, 519 procedures were performed. RESULTS: Of 507 attempted gastrojejunostomy procedures, 482 (95.1%) were successful, 14 (2.8%) catheters could not be advanced through the pylorus and necessitated gastrostomies, and 11 (2.2%) were technical failures. Twelve gastrostomy tubes were placed for decompression, with a 100% success rate. Thirty-day follow-up data were available for 457 procedures: The 30-day mortality rate was 17.1% (71 of 416 patients). There were two gastrostomy-related deaths. The overall major and minor complication rates were 1.3% and 2.9%, respectively. CONCLUSION: Percutaneous gastrostomy and gastrojejunostomy are safe and effective methods of providing short- or long-term enteral nutrition or upper gastrointestinal tract decompression.

Catheterization↗
PubMed1994

Cerebral hemodynamics: monitoring arteriojugular oxygen content differences.

Arteriojugular oxygen difference (AJDO2) is used to manage the care of acute head-injured patients by monitoring the relationship between cerebral metabolism and blood flow. Blood samples from the jugular bulb and a peripheral artery are monitored either continuously or episodically to calculate AJDO2 and cerebral oxygen utilization. An understanding of cerebral oxygen transport physiology is essential to measuring AJDO2. A case study highlights the use of AJDO2 monitoring.

Adolescent↗
PubMed1992

Non-invasive techniques for the measurement of extraction fraction and permeability surface area product of 99Tcm DTPA in the human forearm.

Only a very limited number of clinical studies have been reported on the measurement of endothelial permeability to hydrophilic solutes (molecular weight less than 6000 Daltons) that normally gain free access to the extravascular space. Because of high extraction efficiencies into the extravascular space, the transfer rates of small solutes of molecular weight about 500 Daltons, like 99Tcm DTPA, are perfusion-dependent as well as diffusion-dependent. We describe non-invasive techniques for measurement of clearance and extraction fraction of 99Tcm DTPA into the extravascular space of the resting forearm using a scintillation probe, from which we then calculated permeability surface area (PS) product. Our values for extraction fraction of about 0.5 and for PS product of about 3 ml per minute per 100 ml tissue are comparable to the values reported in the literature for resting skeletal muscle using more invasive techniques.

Capillary Permeability↗
PubMed1992

Platelet imaging of thromboembolism. Natural history of postoperative deep venous thrombosis and pulmonary embolism illustrated using the 111In-labelled platelet-specific monoclonal antibody, P256.

BACKGROUND: Deep venous thrombosis (DVT) and pulmonary thromboembolic disease are difficult to diagnose, particularly following surgery. This report demonstrates the use of 111In-labelled platelet-specific monoclonal antibody, P256 Fab', for the diagnosis and study of the time course of thromboembolic disease in a patient following total hip replacement. METHOD: One hundred micrograms of pentetic acid (DTPA)-P256 Fab' was labelled with 8 to 10 MBq of 111In chloride by incubation at room temperature for 15 min. After dilution in physiologic saline, the tracer was injected intravenously on the third and sixth days postoperatively. Imaging of the chest, pelvis, and legs was carried out at 24, 48 and 72 h following each injection. RESULTS: The first image four days after surgery demonstrated activity in the right heart which moved to the right pulmonary artery on the following day. Activity was seen in both femoral veins; on the left, this increased over two days, followed by a reduction on the seventh day after surgery, at which time new activity was seen in the right heart. After a further two days, this activity moved to the left pulmonary artery. The DVT was confirmed by venography and the pulmonary embolism (PE) by ventilation perfusion scan. CONCLUSIONS: 111Indium-labelled platelet-specific monoclonal antibody, P256 Fab', provides a technique for studying the natural history of thromboembolic disease and its treatment.

Aged↗
PubMed1991

tRNAs of Trypanosoma brucei. Unusual gene organization and mitochondrial importation.

In Trypanosoma brucei the U snRNA B gene (J. C. Mottram, K. L. Perry, P. M. Lizardi, R. Lührmann, N. Agabian, and R. G. Nelson (1989) Mol. Cell. Biol. 9, 1212-1223) is very tightly linked with other small RNA genes coding for tRNA(ACGArg), tRNA(CUULys), and a approximately 275-nucleotide RNA (RNA X) of unknown function. A similar genomic organization is found at the U6 snRNA locus, where the U6 gene is linked to tRNA(CGUThr) and tRNA(GUATyr) genes. The tRNA(Lys) and tRNA(Arg) genes are members of a multigene family, whereas the tRNA(Thr) and tRNA(Tyr) genes are single copy. Two additional tRNA(CUULys) genes and one tRNA(UUULys) gene were also isolated and sequenced and, together with a sequence previously published (D. A. Campbell (1989) Nucleic Acids Res. 17, 9479), appear to represent the entire gene family. Probes for tRNA(Lys), tRNA(Arg), tRNA(Thr), and tRNA(Tyr) were found to hybridize with mitochondrial and cytoplasmic tRNAs but not with mitochondrial DNA. This supports the hypothesis that mitochondrial tRNAs may be nuclear-encoded and imported from the cytosol into the mitochondrion.

Animals↗
PubMed1991

Extravascular chest wall technetium 99m diethylene triamine penta-acetic acid: implications for the measurement of renal function during renography.

Measurement of individual kidney glomerular filtration rate (IKGFR) from the gamma-camera technetium 99m diethylene triamine penta-acetic acid (99mTc-DTPA) renogram requires a continuous measurement of arterial activity. This is usually based on a region of interest (ROI) placed over the cardiac blood pool on the posterior view, with the assumption of negligible contamination from activity in the extravascular space of the chest wall. By injecting a small dose of technetium 99m human serum albumin (HSA) before the 99mTc-DTPA in 12 patients undergoing routine renography, the contribution of extravascular activity to the total signal recorded over the cardiac blood pool was calculated to be 11.0% (SE 2.1%) 1.5 min after DTPA injection, rising to 35.1% (SE 2.5%) at 15 min. Subtraction of the time-activity curve recorded from a ROI of the same size over the right lung generated a "pure" blood signal as shown by almost identical HSA/DTPA signal ratios recorded in blood samples taken 5 min after HSA and 15 min after DTPA and from the gamma-camera at the corresponding times. The effect of using a cardiac blood pool time-activity curve uncorrected for extravascular activity was to overestimate IKGFR by an average factor of 1.17 (SE 0.03).

Glomerular Filtration Rate↗
PubMed1991

Measurement of blood flow from first-pass radionuclide angiography: influence of bolus volume.

Fractionation of cardiac output on first-pass radionuclide angiography is a recently described technique for measuring blood flow. In order to determine the influence of bolus volume, splenic blood flow (SBF) and renal blood flow (RBF) were measured from widely differing bolus volumes given in sequence over a period of a few minutes in patients undergoing routine bone scintigraphy with technetium 99m methylene diphosphonate. A bolus volume of 0.5 ml, followed by 20 ml of rapidly delivered saline "chaser", was regarded as a "gold standard" bolus. A 50 ml bolus, but not a 20 ml bolus, resulted in a significant underestimation of both SBF and RBF. Thus, using a left ventricular region of interest to generate an arterial first-pass time-activity curve, RBF from a 50 ml bolus was 58% (SEM 4%) that given by a 0.5 ml bolus, while RBF for a 20 ml bolus was 98% (8%). Corresponding values for SBF were 52% (10%) and 102% (12%). A quality control adjustment did not correct the underestimation given by the 50 ml bolus. Bolus volumes greater than 20 ml give unreliable estimates of organ blood flow by this technique.

Bone and Bones↗
PubMed1991

The effect of repeated endotracheal suctioning on arterial blood pressure.

The purpose of this study was to examine the effects of three lung hyperinflation/suction sequences on mean arterial pressure (MAP). The results indicate both lung hyperinflation (LHS) and suction sequences (SS) significantly increased MAP (p = .05) from baseline. There was a mean increase in MAP of 13.72 mm Hg over the three lung hyperinflation/suction sequences. The results showed a significant increase in MAP from baseline between SS1 to LHS2 (3.62 mm Hg), from LHS2 to SS2 (4.36 mm Hg), and from LHS3 to SS3 (2.84 mm Hg) at p = .05. The increase in MAP was cumulative with each successive lung hyperinflation/suction sequence. Consequently, the number of repeated lung hyperinflation/suction episodes should be limited to only those necessary to maintain airway patency.

Adult↗