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At least 163 records · Page 9Linked to original sources
PubMed1992

Competition of aminoacyl-tRNA synthetases for tRNA ensures the accuracy of aminoacylation.

The accuracy of protein biosynthesis rests on the high fidelity with which aminoacyl-tRNA synthetases discriminate between tRNAs. Correct aminoacylation depends not only on identity elements (nucleotides in certain positions) in tRNA (1), but also on competition between different synthetases for a given tRNA (2). Here we describe in vivo and in vitro experiments which demonstrate how variations in the levels of synthetases and tRNA affect the accuracy of aminoacylation. We show in vivo that concurrent overexpression of Escherichia coli tyrosyl-tRNA synthetase abolishes misacylation of supF tRNA(Tyr) with glutamine in vivo by overproduced glutaminyl-tRNA synthetase. In an in vitro competition assay, we have confirmed that the overproduction mischarging phenomenon observed in vivo is due to competition between the synthetases at the level of aminoacylation. Likewise, we have been able to examine the role competition plays in the identity of a non-suppressor tRNA of ambiguous identity, tRNA(Glu). Finally, with this assay, we show that the identity of a tRNA and the accuracy with which it is recognized depend on the relative affinities of the synthetases for the tRNA. The in vitro competition assay represents a general method of obtaining qualitative information on tRNA identity in a competitive environment (usually only found in vivo) during a defined step in protein biosynthesis, aminoacylation. In addition, we show that the discriminator base (position 73) and the first base of the anticodon are important for recognition by E. coli tyrosyl-tRNA synthetase.

Amino Acyl-tRNA Synthetases↗
PubMed1999

Dopamine D3 agonists into the substantia nigra aggravate cataplexy but do not modify sleep.

We have recently demonstrated that local perfusion of dopaminergic D2/D3 agonists into the ventral tegmental area (VTA) significantly aggravates cataplexy and increases sleep in narcoleptic Dobermans. We further assessed the roles of the mesostriatal dopaminergic system and found that local perfusion of quinpirole and 7-OH-DPAT into the substantia nigra (SN) significantly aggravated cataplexy, while perfusion of a D2/D3 antagonist significantly reduced cataplexy. Neither a D1 agonist nor a D1 antagonist modified cataplexy. SN perfusion of quinpirole did not significantly modify sleep, while VTA perfusion significantly increased the drowsy state. Although autoregulation of the VTA and SN dopaminergic neurons are involved in the regulation of cataplexy, both structures have distinct roles for the regulation of sleep.

Animals↗
PubMed1989

The effect of office visit copayments on utilization in a health maintenance organization.

This study estimated the impact of a $5 copayment on office visit rates in a health maintenance organization. A quasi-experimental design was used to compare the observed changes in visit rates by state government enrollees between the year before copayments and their first year of copayments with changes between the same time periods for a control group of enrollees without copayments. Visit data for 30,415 state enrollees and 21,633 federal enrollees who were enrolled continuously for at least 12 months before and after the start of copayments were obtained from automated data systems. The introduction of a $5 copayment for office visits resulted in an estimated 10.9% decrease in primary care visits (95% confidence interval (CI): -13.4% to -8.4%) and a 3.3% drop in specialty care visits (95% CI: -15.6% to +9.0%). The effect of copayments on primary care visits by enrollees under 40 years of age was twice as large for females as for males. Copayments also had a significantly greater impact on enrollees who were high users (greater than ten primary care visits) during the year before copayments. The copayment effect was immediate and did not diminish over the 12-month study period.

Adolescent↗
PubMed1997

Rpp1, an essential protein subunit of nuclear RNase P required for processing of precursor tRNA and 35S precursor rRNA in Saccharomyces cerevisiae.

The gene for an essential protein subunit of nuclear RNase P from Saccharomyces cerevisiae has been cloned. The gene for this protein, RPP1, was identified by virtue of its homology with a human scleroderma autoimmune antigen, Rpp30, which copurifies with human RNase P. Epitope-tagged Rpp1 can be found in association with both RNase P RNA and a related endoribonuclease, RNase MRP RNA, in immunoprecipitates from crude extracts of cells. Depletion of Rpp1 in vivo leads to the accumulation of precursor tRNAs with unprocessed 5' and 3' termini and reveals rRNA processing defects that have not been described previously for proteins associated with RNase P or RNase MRP. Immunoprecipitated complexes cleave both yeast precursor tRNAs and precursor rRNAs.

Amino Acid Sequence↗
PubMed2002

A new high resolution color flow system using an eigendecomposition-based adaptive filter for clutter rejection.

We present a new signal processing strategy for high frequency color flow mapping in moving tissue environments. A new application of an eigendecomposition-based clutter rejection filter is presented with modifications to deal with high blood-to-clutter ratios (BCR). Additionally, a new method for correcting blood velocity estimates with an estimated tissue motion profile is detailed. The performance of the clutter filter and velocity estimation strategies is quantified using a new swept-scan signal model. In vivo color flow images are presented to illustrate the potential of the system for mapping blood flow in the microcirculation with external tissue motion.

Algorithms↗
PubMed1995

Retinoic acid regulates oral epithelial differentiation by two mechanisms.

The effect of retinoic acid (RA) concentration on differentiation of oral keratinocytes and the influence of fibroblasts on RA-dependent regulation were investigated in a lifted culture system. Keratinocyte differentiation was assessed by morphology, immunohistochemistry and immunoblotting. Filaggrin/profilaggrin and keratin 1 were used as biochemical markers for cornified epithelium and keratins 13 and 19 as markers for noncornified epithelium. Cultured oral keratinocytes in RA-free conditions differentiated in a manner that closely resembled the differentiation pattern of gingival epithelia in vivo. Increasing RA concentrations altered the in vivo-like terminal differentiation of oral keratinocytes by disruption of organized stratification, inhibition of filaggrin/profilaggrin and K1 expression, and stimulation of K13 and K19 expression. Differentiation of keratinocytes from both cornified and noncornified regions of the oral cavity varied in a similar manner in response to added RA, with the exception of K19 expression. K19 was consistently expressed at higher levels in keratinocytes originating from noncornified epithelial as compared to those from cornified epithelia. The level of RA regulation was ultimately dependent on the type of fibroblasts underlying the epithelial cells. Homologous fibroblasts rendered the oral keratinocytes less sensitive to the effects of RA than skin fibroblasts. In addition, at a given RA concentration, fibroblasts from cornified oral mucosa potentiated keratinocyte expression of RA sensitive markers of keratinization as compared to the influence exerted by fibroblasts originating from noncornified oral mucosa. These results indicate that the RA regulation of oral epithelial differentiation is mediated by two separate mechanisms: a direct, RA concentration-dependent effect, and an indirect, fibroblast-mediated effect.

Cell Differentiation↗
PubMed1997

African-American HLA class II allele and haplotype diversity.

Molecular genetic techniques were used to type nine loci in the HLA class II region in 241 unrelated African-Americans from New York City (NYC). Several effects attributable to recent genetic admixture were evident: the number of distinct class II alleles and haplotypes was larger in the African-Americans than in people of African or European origin, the allele frequencies were more consistently even, and linkage disequilibrium was present across the entire class II region. The African-American DRB1 allele frequencies almost always fell between frequencies among samples from northern Europe and the Gambia, two possible founding populations. The exceptions are attributed to the contribution of other genetically dissimilar African groups to the African-American gene pool. DRB1 allele frequencies (specifically DRB1*1501) and some haplotypes of DRB1-DPB1 were different in our NYC and the 11th International Histocompatibility Workshop (IHW) samples of African-Americans. The high level of allele and haplotype diversity found in African-Americans has important implications for the construction of pools of unrelated potential donors for tissue transplantation.

Alleles↗
PubMed2000

Secretagogue response of goblet cells and columnar cells in human colonic crypts.

Crypts of Lieberkühn were isolated from human colon, and differential interference contrast microscopy distinguished goblet and columnar cells. Activation with carbachol (CCh, 100 microM) or histamine (10 microM) released contents from goblet granules. Stimulation with prostaglandin E(2) (PGE(2), 5 microM) or adenosine (10 microM) did not release goblet granules but caused the apical margin of columnar cells to recede. Goblet volume was lost during stimulation with CCh or histamine ( approximately 160 fl/cell), but not with PGE(2) or adenosine. Three-quarters of goblet cells were responsive to CCh but released only 30% of goblet volume. Half-time for goblet volume release was 3.7 min. PGE(2) stimulated a prolonged fluid secretion that attained a rate of approximately 350 pl/min. Columnar cells lost approximately 50% of apical volume during maximal PGE(2) stimulation, with a half-time of 3.3 min. In crypts from individuals with ulcerative colitis, goblet cells were hypersensitive to CCh for release of goblet volume. These results support separate regulation for mucus secretions from goblet cells and from columnar cells, with control mechanisms restricting total release of mucus stores.

Adenosine↗
PubMed2000

Overlapping corticostriatal projections from the rodent vibrissal representations in primary and secondary somatosensory cortex.

To determine whether the neostriatum receives overlapping projections from two somatosensory cortical areas, the anterograde tracers biotinylated dextran amine (BDA) and fluoro-ruby (FR) were injected into the whisker representations of primary (SI) and secondary (SII) somatosensory cortex. Reconstructions of labeled terminals and their beaded varicosities in the neostriatum and thalamus were analyzed quantitatively to compare the extent of overlapping projections to both subcortical structures. Corticostriatal projections from focal sites in both somatosensory areas exhibited substantial amounts of divergence within the dorsolateral neostriatum. Most of the labeled terminals were concentrated in densely packed arborizations that occupied lamellar-shaped regions along the dorsolateral edge of the neostriatum. Tracer injections in both cortical areas also produced dense anterograde and retrograde labeling in the thalamus, especially in the ventrobasal complex (VB) and in the medial part of the posterior (POm) nucleus. Because these thalamic regions are topographically organized and have reciprocal connections with corresponding representations in both SI and SII, the amount of labeled overlap in the thalamus was used to indicate the degree of somatotopic correspondence at the SI and SII injection sites. We found that the proportion of overlapping projections to the neostriatum was moderately correlated with the amount of overlap observed in the thalamus. This result strongly indicates that specific sites in the dorsolateral neostriatum receive convergent projections from corresponding somatotopic representations in SI and SII, but also suggests that some of the corticostriatal divergence may reflect neostriatal integration of somatosensory information from noncorresponding representations in SI and SII.

Animals↗
PubMed2001

Building a gateway to promote cardiovascular health research in African American communities: lessons and findings from the field.

African American communities traditionally mistrust academic research. This forms a significant barrier to understanding cardiovascular risk factors in this population, which bears an excess risk of cardiovascular disease and stroke. A clergy/academic partnership was established to build a gateway for salient research and for improving resources for reducing cardiovascular disease risk in the community. From this partnership emanated the African American Family Heart Study. People with a family history of premature coronary heart disease (CHD) have an increased risk for the disease--as high as 12 times that of the general population, if among siblings. Considerably less is known about the actual remediable risk factors in African American families with premature CHD. We initiated the Family Heart Study with a full characterization of 161 apparently healthy, unaffected 30- to 59-year-old African Americans whose siblings were 85 African American index cases with documented premature CHD prior to 60 years of age. We compared their risk factor values to population reference norms obtained in the Third National Health and Nutrition Examination Survey (NHANES III) and the National Health Interview Survey (NHIS) for cigarette smoking. Only 13% of African American male siblings and 14% of female siblings from these families were without any major remediable risk factors. The fact that so many siblings were at extremely high risk calls into question the current applications by provider systems of national guidelines in high-risk African American families. This is an easily identifiable population that would be likely to benefit greatly from targeted screening and culturally sensitive and appropriate treatment.

Adult↗
PubMed2003

Surgeons, intensivists, and the covenant of care: administrative models and values affecting care at the end of life--Updated.

CONTEXT: End-of-life care remains a challenging and complex activity in critical care units. There is little information concerning the influence of administrative models of care delivery on end-of-life care. OBJECTIVE: To compare and contrast end-of-life care delivery in intensive care units using "semiclosed," "open," and "closed" administrative models. DESIGN: Ethnographic study of three critical care units. SETTING: University hospitals in the United States and New Zealand. SUBJECTS: Approximately 600 physicians, nurses, allied health personnel, patients, family members, and friends. MEASUREMENTS AND MAIN RESULTS: Ethnographic observations were made at three sites for 75, 3, and 10 wks, respectively. Eighty end-of-life care episodes were observed. The interactions among care personnel and families varied according to the administrative model, depending on whether surgeons or intensivists had primary patient responsibility. This led to differential timing on the shift from "cure" to "comfort," and differential decision-making power for families. CONCLUSIONS: End-of-life care varies according to the administrative model. When surgeons have primary responsibility for the patient, the most important goal is defeating death. When intensivists have sole patient responsibility, scarce resources are considered and quality of life is a significant variable. Discussions about improving the way end-of-life decisions are carried out in intensive care units rarely consider the administrative models and personal, professional, and national values affecting such decisions. To improve care at the end of life, we must critically examine these features.

Anthropology, Cultural↗
PubMed2003

Parallel evolution by gene duplication in the genomes of two unicellular fungi.

Phylogenetic analysis of conserved gene families in fission yeast Schizosaccharomyces pombe and brewer's yeast Saccharomyces cerevisiae showed that gene duplications have occurred independently in the same families in each of these two lineages to a far greater extent than expected by chance. These species represent distinct lineages of the phylum Ascomycota that independently evolved a "yeast" life cycle with a unicellular thallus that reproduces by budding, and many of the genes that have duplicated independently in the two lineages are known to be involved in crucial aspects of this life cycle. Parallel gene duplication thus appears to have played a role in the independent origin of similar adaptations in the two species. The results indicate that using phylogenetic analysis to test for parallel gene duplication in different species may help in identifying genes responsible for similar but independently evolved adaptations

Evolution, Molecular↗
PubMed1990

The effects of chronic caffeine administration on peripheral adenosine receptors.

Rat platelets and adipocytes were used as models to investigate alterations of the A2- and of the A1-adenosine receptor-adenylate cyclase system of peripheral cells caused by chronic caffeine administration. The maximum effects of 5'-N-ethylcarboxamidoadenosine (NECA) to stimulate adenylate cyclase activity in suspensions of platelet membranes and to inhibit aggregation were significantly greater with platelets from caffeine-treated rats than from control rats. The effects of 1 to 100 nM prostaglandin E1 to inhibit platelet aggregation and to stimulate adenylate cyclase activity in platelet membranes were also significantly greater with caffeine-treated than with control rats. These data suggest that the increased ability of NECA to inhibit platelet aggregation after chronic caffeine ingestion was a result of increased cyclic AMP accumulation induced by this agonist. The increased stimulatory effect of NECA on adenylate cyclase in platelet membranes could be due to an increased A2-adenosine receptor number and/or an increased functional coupling between A2-adenosine receptor and stimulatory guanine nucleotide binding proteins. In contrast, although A1-receptor number was 37% higher in fat cell membranes from caffeine-treated rats than in those from control rats, increased A1-adenosine receptor-mediated inhibition of lipolysis and of adenylate cyclase was not detected. Thus, chronic caffeine consumption causes alterations in the response of some but not all peripheral cell types to agonists of adenosine receptors.

Adenylyl Cyclases↗
PubMed1997

Identification of a new coiled body component.

Coiled bodies are small, round nuclear inclusions that have been identified in many somatic cell types. Equivalent structures are found in the germinal vesicles of amphibian and insect oocytes, known respectively as sphere organelles and Binnenkörper. Their functions are not known, but their molecular composition is being brought to light. In addition to the nucleolar protein, fibrillarin, coiled bodies contain DNA topoisomerase I and an array of RNA processing molecules characteristic of spliceosomes. One coiled body protein absent from nucleoli and spliceosomes, known as p80-coilin, has also been described. We have now identified pigpen, a new member of the EWS family of proteins, as a second protein enriched in coiled bodies. In an earlier report we found that pigpen's structure and expression pattern were suggestive of a role in endothelial cell proliferation and differentiation. In this brief report we characterize pigpen's nuclear compartment and describe its reorganization during mitosis.

Animals↗
PubMed2002

The reproductive importance of P-type ATPases.

P-type ATPases are integral membrane proteins that use the free energy of ATP hydrolysis to generate transmembrane electrochemical ion gradients to support a variety of cellular processes. They have eight signature motifs, eight or ten transmembrane domains, highly conserved phosphorylation and ATP-binding sites, and similar hydropathic profiles. This review summarizes recent insights in the relationship of P-type ATPases to successful reproduction, and the hormone dependence of some family members. Because protein topology is central to understanding the pump action of this family of enzymes, this review also describes the dramatic change in the primary structure of one family member that may mediate transcription in the uterus.

Adenosine Triphosphatases↗
PubMed1997

Roles of phospholipases A2 in brain cell and tissue injury associated with ischemia and excitotoxicity.

Phospholipase A2 (PLA2) activity is an important contributor to destructive cellular processes in the central nervous system. Two cytosolic forms of calcium dependent PLA2 have been characterized in the gerbil brain and the neuronal cultures from rat brain. PLA2 enzymatic activity in cell free extracts from cortical neuronal cultures is upregulated after cells are exposed to glutamate. Brief exposure to a calcium ionophore or phorbol 12-myristate 13-acetate (PMA) stably enhanced PLA2 activity. Stable activation of the two cytosolic forms of PLA2 occur prior to evidence of cell death and this activation is reversible. The larger molecular mass form was characterized as cPLA2. The smaller form (approximately 14 kDa) was distinct from Group I and II PLA2. Exposure to glutamate shifted the calcium activation curve of the smaller form to the left suggesting a novel mechanism of regulation of PLA2. Glutamate-induced stable enhancement of PLA2 activity, by processes involving calcium and protein kinase C activation, is a potential molecular switch likely mediating changes in synaptic function and contributing to excitotoxicity.

Animals↗