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Biomedical subjects

G R Smith

Publications and source records attributed to G R Smith.

At least 55 records · Page 3Linked to original sources
PubMed1999

Effective diffusion coefficients of K+ and Cl- ions in ion channel models.

We have used molecular dynamics simulations, corresponding to a total simulation time of 11 ns, to investigate the effective short-time local diffusion coefficient of potassium and chloride ions in a series of model ion channels. These models, which include channels formed by the fungal peptide alamethicin, by a synthetic leucine-serine peptide, and by the pore-lining M2 helix bundle of the nicotinic acetylcholine receptor, have a range of different secondary structures, diameters and hydrophobicities. We find that the diffusion coefficients of both ions are appreciably reduced in the narrower channels, the extent of the reduction being similar for both the anionic and cationic species. This suggests that a difference in mobility cannot be the source of the ion selectivity exhibited by some of the channels (for example, the leucine-serine peptide). We find no evidence for a reduction in mobility of either ion in the nAChR model. These results are broadly in line with a previous similar study of Na+ ions, and may be useful in Poisson-Nernst-Planck, Eyring rate theory or Brownian dynamics calculations of channel conductance.

Chlorides↗
PubMed1999

Regulation of homologous recombination: Chi inactivates RecBCD enzyme by disassembly of the three subunits.

We report here an unusual mechanism for enzyme regulation: the disassembly of all three subunits of RecBCD enzyme after its interaction with a Chi recombination hot spot. The enzyme, which is essential for the major pathway of recombination in Escherichia coli, acts on linear double-stranded DNA bearing a Chi site to produce single-stranded DNA substrates for strand exchange by RecA protein. We show that after reaction with DNA bearing Chi sites, RecBCD enzyme is inactivated and the three subunits migrate as separate species during glycerol gradient ultracentrifugation or native gel electrophoresis. This Chi-mediated inactivation and disassembly of purified RecBCD enzyme can account for the previously reported Chi-dependent loss of Chi activity in E. coli cells containing broken DNA. Our results support a model of recombination in which Chi regulates one RecBCD enzyme molecule to make a single recombinational exchange ('one enzyme-one exchange' hypothesis).

Adenosine Triphosphate↗
PubMed1999

Treatment of depression in rural Arkansas: policy implications for improving care.

Policy-makers have long suspected that greater barriers to care result in depressed rural residents being less likely to receive high-quality treatment. This study recruited 470 depressed community residents in a 1992 telephone survey, followed 95 percent of them through one year, and abstracted additional data on their health care utilization from insurance claims, medical and pharmacy records. Bivariate and multivariate models demonstrated that during the year following the baseline, there were no significant rural-urban differences in the rate (probability of any outpatient depression treatment), type (probability of receiving general medical depression care only), or quality (completion of guideline-concordant acute-stage care) of outpatient depression treatment. Annual expenditures for outpatient depression treatment were lower for rural subjects compared with their urban counterparts. Rural subjects had 3.05 times the odds of being admitted to a hospital for physical problems and 3.06 times the odds of being admitted to a hospital for mental health problems during the year following baseline compared with urban subjects. Cost-offset analyses demonstrate that every dollar invested in depression treatment was associated with a $2.61 decrease in the cost of treating physical problems in depressed rural residents. Limited insurance coverage and limited availability of services were the most significant barriers to specialty and general medical outpatient treatment for depression in both rural and urban residents. More than 80 percent of depressed residents in both rural and urban areas visited a primary care provider during the year following baseline. The potential cost offset of depression treatment in rural populations plus the improvement in productivity observed in both rural and urban populations indicate that it may be economically possible to improve quality of care for depression without bankrupting an already strained health care budget.

Adult↗
PubMed1999

A community study of depression treatment and employment earnings.

OBJECTIVE: Although treatment for major depression has been shown to reduce the costs of lost earnings resulting from lost work days, research has not demonstrated whether the reduction fully offsets the costs of treatment for the disorder. METHODS: A statewide cohort of community residents with recent major depression, dysthymia, or substantial depressive symptoms was recruited and interviewed at baseline and at six-month and 12-month follow-ups. The cost of lost earnings was measured by lost work days multiplied by subjects' wage rates. Cost of treatment for depression was approximated using charges abstracted from provider and insurance records. Net economic cost, defined as the sum of changes in lost earnings and depression treatment costs, was examined in multiple regression analyses. RESULTS: After the analyses controlled for sociodemographic characteristics, baseline severity of depression, and comorbidity, no statistically significant effect of depression treatment on net economic cost was found. This finding suggests that the cost of depression treatment was fully offset by savings from reduction in lost work days. Results from sensitivity analyses in multiple alternative scenarios support the same conclusion. CONCLUSIONS: The finding of a full offset of depression treatment cost is conservative because other benefits, such as reduced pain and suffering and increased productivity while at work, were not included in the analyses. Employers who bear the cost from lost work days should encourage their employees with depressive disorders to seek treatment, even if it means paying for the entire treatment cost. Self-employed individuals with depression also will benefit even if they pay for the treatment costs themselves.

Absenteeism↗
PubMed1999

Project leadership: why project management alone doesn't work.

Projects often fall short of achieving their anticipated results, not due to a lack of project management, but rather from a lack of project leadership. Because project success is a direct reflection of the project manager, it is his or her responsibility not just to manage the details and report status of a project, but to go beyond and add value through providing leadership. Project managers can no longer update task lists and issue meeting minutes if they are to succeed. This article focuses on adapting proven leadership strategies to project environments, helping to increase the probability for project success. When properly applied, they will help turn today's project manager into tomorrow's project leader.

Attitude to Computers↗
PubMed1998

A stimulatory RNA associated with RecBCD enzyme.

RecBCD enzyme acts in the major pathway of homologous recombination of linear DNA in Escherichia coli. The enzyme unwinds DNA and is an ATP-dependent double-strand and single-strand exonuclease and a single-strand endonuclease; it acts at Chi recombination hotspots (5'-GCTGGTGG-3') to produce a recombinogenic single-stranded DNA 3'-end. We found that a small RNA with a unique sequence of approximately 24 nt was tightly bound to RecBCD enzyme and co-purified with it. When added to native enzyme this RNA, but not four others, increased DNA unwinding and Chi nicking activities of the enzyme. In seven similarly active enzyme preparations the molar ratio of RNA molecules to RecBCD enzyme molecules ranged from 0.2 to <0.008. These results suggest that, although this unique RNA is not an essential enzyme subunit, it has a biological role in stimulating RecBCD enzyme activity.

DNA Helicases↗
PubMed1998

Modification of bacterial artificial chromosomes through chi-stimulated homologous recombination and its application in zebrafish transgenesis.

The modification of yeast artificial chromosomes through homologous recombination has become a useful genetic tool for studying gene function and enhancer/promoter activity. However, it is difficult to purify intact yeast artificial chromosome DNA at a concentration sufficient for many applications. Bacterial artificial chromosomes (BACs) are vectors that can accommodate large DNA fragments and can easily be purified as plasmid DNA. We report herein a simple procedure for modifying BACs through homologous recombination using a targeting construct containing properly situated Chi sites. To demonstrate a usage for this technique, we modified BAC clones containing the zebrafish GATA-2 genomic locus by replacing the first coding exon with the green fluorescent protein (GFP) reporter gene. Molecular analyses confirmed that the modification occurred without additional deletions or rearrangements of the BACs. Microinjection demonstrated that GATA-2 expression patterns can be recapitulated in living zebrafish embryos by using these GFP-modified GATA-2 BACs. Embryos microinjected with the modified BAC clones were less mosaic and had improved GFP expression in hematopoietic progenitor cells compared with smaller plasmid constructs. The precise modification of BACs through Chi-stimulated homologous recombination should be useful for studying gene function and regulation in cultured cells or organisms where gene transfer is applicable.

Animals↗
PubMed1998

Protein-water-ion interactions in a model of the pore domain of a potassium channel: a simulation study.

A model of the selectivity filter of a voltage-gated K+ (Kv) channel formed by an eight-stranded beta-barrel is compared with physiological properties of the channel. Continuum electrostatic calculations suggest that only two of the eight Asp sidechains at the extracellular mouth of the pore will ionise. A ring of four Tyr sidechains forms the narrowest region of the pore. Molecular dynamic simulations of the potential energy of a K+ ion as translated along the model pore indicate that the two ionised Asp sidechains and the hydroxyl groups of the Tyr sidechains stabilise the partially desolvated ion as it passes through the narrowest region.

Amino Acid Sequence↗
PubMed1998

Modelling and simulation of ion channels: applications to the nicotinic acetylcholine receptor.

Molecular dynamics simulations with experimentally derived restraints have been used to develop atomic models of M2 helix bundles forming the pore-lining domains of the nicotinic acetylcholine receptor and related ligand-gated ion channels. M2 helix bundles have been used in microscopic simulations of the dynamics and energetics of water and ions within an ion channel. Translational and rotational motion of water are restricted within the pore, and water dipoles are aligned relative to the pore axis by the surrounding helix dipoles. Potential energy profiles for translation of a Na+ ion along the pore suggest that the protein and water components of the interaction energy exert an opposing effect on the ion, resulting in a relatively flat profile which favors cation permeation. Empirical conductance calculations based on a pore radius profile suggest that the M2 helix model is consistent with a single channel conductance of ca. 50 pS. Continuum electrostatics calculations indicate that a ring of glutamate residues at the cytoplasmic mouth of the alpha 7 nicotinic receptor M2 helix bundle may not be fully ionized. A simplified model of the remainder of the channel protein when added to the M2 helix bundle plays a significant role in enhancing the ion selectivity of the channel.

Amino Acid Sequence↗
PubMed1998

Services utilization before and after the prospective payment system by patients with somatization disorder.

This study analyzed services utilization before and after the implementation of Medicare's Prospective Payment System (PPS) in psychiatric patients with somatization disorder in two samples: one recruited before the PPS and the other after the PPS. Individuals with this psychiatric disorder present with multiple unexplained medical complaints and consume a great number of health resources. The results from this study indicated that Medicare PPS was associated with fewer hospital admissions and fewer hospital days, with a greater number of physician visits (for Medicare patients) and emergency room visits (for non-Medicare patients) and with lower overall health expenditures. However, there were no significant changes in the average length of stay after PPS. In contrast to previous studies, Medicare PPS was significantly associated with changes in service utilization by non-Medicare patients as well, a possible "spillover effect." This study confirms the results from other research indicating that higher levels of efficiency may be achieved for certain psychiatric disorders through prospective payment mechanisms.

Adult↗
PubMed1998

Global control of meiotic recombination genes by Schizosaccharomyces pombe rec16 (rep1).

The Schizosaccharomyces pombe rec16-125 mutation reduces meiotic recombination, delays premeiotic DNA synthesis, and reduces the accumulation of some but not other rec gene transcripts. To elucidate the function of the Rec16 global meiotic regulator, we cloned and sequenced rec16. The data revealed that rec16 is identical to rep1, which was previously shown to encode a protein with a zinc-finger motif required for pre-meiotic DNA synthesis. Transcripts of rec16 (rep1) were strongly induced and subsequently degraded during meiosis. In a rec16 (rep1) deletion mutant, meiotic induction of the seven rec genes tested, which appear to be directly involved in meiotic recombination, was significantly reduced or essentially abolished. Deletion of 80% of the gene essentially abolished meiotic recombination, whereas strains deleted for approximately one-quarter of the gene, from either end, retained partial activity. The rec16-125 mutation strongly reduced recombination in the intervals tested on chromosomes I and III, a phenotype characteristic of mutations in rec genes, such as rec7, whose expression requires Rec16 (Rep1). These results show that Rec16 (Rep1) does not have the regional specificity of Rec10. We infer that Rec16 (Rep1) is a transcriptional activator that is required for meiotic replication and recombination because it plays a role in the transcriptional induction of the rec and other meiosis-specific genes.

Chromosomes, Fungal↗
PubMed1998

Sequence diversity in the coat protein coding region of twelve sugarcane mosaic potyvirus isolates from Australia, USA and South Africa.

We have sequenced the coat protein (CP) coding region of 11 field isolates of SCMV from Australia, USA and South Africa. The differences between the nucleotide sequences of the isolates was 0.2 to 4.1% and the encoded amino acid sequences differed by 0.0 to 3.5%. Phylogenetic analysis of the CP coding sequences of the SCMV isolates and the related potyviruses SCMV-MDB, JGMV, SrMV, MDMV-A and PVY showed that the SCMV isolates formed a tightly clustered group, with SCMV-MDB forming a separate branch. This indicated that (i) the SCMV isolates are of one strain (SCMV-A) and not geographically distinct species and (ii) SCMV-MDB is clearly distinct, and may represent another potyvirus species.

Amino Acid Sequence↗
PubMed1998

Electrostatics and the ion selectivity of ligand-gated channels.

The nicotinic acetylcholine receptor (nAChR) is a cation-selective ion channel that opens in response to acetylcholine binding. The related glycine receptor (GlyR) is anion selective. The pore-lining domain of each protein may be modeled as a bundle of five parallel M2 helices. Models of the pore-lining domains of homopentameric nAChR and GlyR have been used in continuum electrostatics calculations to probe the origins of ion selectivity. Calculated pKA values suggest that "rings" of acidic or basic side chains at the mouths of the nAChR or GlyR M2 helix bundles, respectively, may not be fully ionized. In particular, for the nAChR the ring of glutamate side chains at the extracellular mouth of the pore is predicted to be largely protonated at neutral pH, whereas those glutamate side chains in the intracellular and intermediate rings (at the opposite mouth of the pore) are predicted to be fully ionized. Inclusion of the other domains of each protein represented as an irregular cylindrical tube in which the M2 bundles are embedded suggests that both the M2 helices and the extramembrane domains play significant roles in determining ion selectivity.

Amino Acid Sequence↗
PubMed1998

Dynamic properties of Na+ ions in models of ion channels: a molecular dynamics study.

We present simulation results for the effective diffusion coefficients of a sodium ion in a series of model ion channels of different diameters and hydrophobicities, including models of alamethicin, a leucine-serine peptide, and the M2 helix bundle of the nicotinic acetylcholine receptor. The diffusion coefficient, which in the simulations has a value of 0.15(2) A2ps-1 in bulk water, is found to be reduced to as little as 0.02(1) A2ps-1 in the narrower channels, and to about 0.10(5) A2ps-1 in wider channels such as the nicotinic acetylcholine receptor. It is anticipated that this work will be useful in connection with calculations of channel conductivity using such techniques as the Poisson-Nernst-Planck equation, Eyring rate theory, or Brownian dynamics.

Alamethicin↗
PubMed1998

Control of meiotic recombination in Schizosaccharomyces pombe.

Homologous recombination occurs at high frequency during meiosis and is essential for the proper segregation of chromosomes and the generation of genetic diversity. Meiotic recombination is controlled in numerous ways. In the fission yeast Schizosaccharomyces pombe nutritional starvation induces meiosis and high-level expression of many genes, including numerous recombination (rec) genes, whose products are required for recombination. Accompanying the two meiotic divisions are profound changes in nuclear and chromosomal structure and movement, which may play an important role in meiotic recombination. Although recombination occurs throughout the genome, it occurs at high frequency in some intervals (hotspots) and at low frequency in others (coldspots). The well-characterized hotspot M26 is activated by the Mts1/Mts2 protein; this site and its binding proteins interact with the local chromosomal structure to enhance recombination. A coldspot between the silent mating-type loci is repressed by identified proteins, which may also alter local chromatin. We discuss in detail the rec genes and the possible functions of their products, some but not all of which share homology with other identified proteins. Although some of the rec gene products are required for recombination throughout the genome, others demonstrate regional specificity and are required in certain genomic regions but not in others. Throughout the review contrasts are made with meiotic recombination in the more thoroughly studied budding yeast Saccharomyces cerevisiae.

Cell Nucleus↗
PubMed1998

Persistently poor outcomes of undetected major depression in primary care.

Despite its relevance for quality care initiatives, the field of psychiatry has little scientific knowledge regarding the course of current major depression when primary care patients with the disorder remain undetected. Using statewide telephone screening, we identified and followed 98 adults with current major depression who made one or more visits to a primary care physician during the 6 months following baseline. Thirty-two percent of primary care patients with current major depression remained undetected for up to 1 year. Almost half of undetected patients developed suicidal ideation. Less than one-third of undetected patients made a visit during the month they reported their worst symptoms. Fifty-three percent of undetected patients reported five or more current symptoms at 1 year follow-up. Primary care patients with undetected major depression report persistently poor outcomes. Comparison of outcomes with detected patients suggests that quality improvement efforts directed at improving detection without improving management of detected patients may not improve outcomes.

Adult↗