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R Yuan

Publications and source records attributed to R Yuan.

At least 55 records · Page 3Linked to original sources
PubMed1997

Glu-tRNAGln amidotransferase: a novel heterotrimeric enzyme required for correct decoding of glutamine codons during translation.

The three genes, gatC, gatA, and gatB, which constitute the transcriptional unit of the Bacillus subtilis glutamyl-tRNAGln amidotransferase have been cloned. Expression of this transcriptional unit results in the production of a heterotrimeric protein that has been purified to homogeneity. The enzyme furnishes a means for formation of correctly charged Gln-tRNAGln through the transamidation of misacylated Glu-tRNAGln, functionally replacing the lack of glutaminyl-tRNA synthetase activity in Gram-positive eubacteria, cyanobacteria, Archaea, and organelles. Disruption of this operon is lethal. This demonstrates that transamidation is the only pathway to Gln-tRNAGln in B. subtilis and that glutamyl-tRNAGln amidotransferase is a novel and essential component of the translational apparatus.

Acylation↗
PubMed1997

A role for the disintegrin domain of cyritestin, a sperm surface protein belonging to the ADAM family, in mouse sperm-egg plasma membrane adhesion and fusion.

Sperm-egg plasma membrane fusion is preceded by sperm adhesion to the egg plasma membrane. Cell-cell adhesion frequently involves multiple adhesion molecules on the adhering cells. One sperm surface protein with a role in sperm-egg plasma membrane adhesion is fertilin, a transmembrane heterodimer (alpha and beta subunits). Fertilin alpha and beta are the first identified members of a new family of membrane proteins that each has the following domains: pro-, metalloprotease, disintegrin, cysteine-rich, EGF-like, transmembrane, and cytoplasmic domain. This protein family has been named ADAM because all members contain a disintegrin and metalloprotease domain. Previous studies indicate that the disintegrin domain of fertilin beta functions in sperm-egg adhesion leading to fusion. Full length cDNA clones have been isolated for five ADAMs expressed in mouse testis: fertilin alpha, fertilin beta, cyritestin, ADAM 4, and ADAM 5. The presence of the disintegrin domain, a known integrin ligand, suggests that like fertilin beta, other testis ADAMs could be involved in sperm adhesion to the egg membrane. We tested peptide mimetics from the predicted binding sites in the disintegrin domains of the five testis-expressed ADAMs in a sperm-egg plasma membrane adhesion and fusion assay. The active site peptide from cyritestin strongly inhibited (80-90%) sperm adhesion and fusion and was a more potent inhibitor than the fertilin beta active site peptide. Antibodies generated against the active site region of either cyritestin or fertilin beta also strongly inhibited (80-90%) both sperm-egg adhesion and fusion. Characterization of these two ADAM family members showed that they are both processed during sperm maturation and present on mature sperm. Indirect immunofluorescence on live, acrosome-reacted sperm using antibodies against either cyritestin or fertilin beta showed staining of the equatorial region, a region of the sperm membrane that participates in the early steps of membrane fusion. Collectively, these data indicate that a second ADAM family member, cyritestin, functions with fertilin beta in sperm-egg plasma membrane adhesion leading to fusion.

ADAM Proteins↗
PubMed1997

CCAAT/enhancer-binding protein-delta (C/EBP-delta) is induced in growth-arrested mouse mammary epithelial cells.

CCAAT/enhancer binding proteins (C/EBPs) are a highly conserved family of DNA-binding proteins that regulate cell growth and differentiation in a highly tissue-specific manner. These experiments investigated the influence of the cell cycle on C/EBP isoform expression in mammary epithelial cells (COMMA D) and fibroblasts (NIH3T3). C/EBP-delta gene expression is induced in COMMA D cells arrested in G0 by serum and growth factor withdrawal or contact inhibition. C/EBP-delta mRNA, nuclear protein content, and DNA binding activity increase during G0 growth arrest and decrease after cell cycle induction in COMMA D cells. Growth arrest is markedly delayed in COMMA D cells expressing a C/EBP-delta antisense construct. C/EBP-beta is induced during G1 of the cell cycle. In contrast to COMMA D cells, C/EBP-beta and C/EBP-delta mRNA levels remain relatively constant in growth-arrested and cell cycle-induced NIH3T3 cells. However, C/EBP homologous protein (CHOP10) mRNA levels markedly increase in growth-arrested NIH3T3 cells. Both COMMA D and NIH3T3 cells express growth arrest-specific (gas1) and JunD during G0. These results demonstrate that COMMA D and NIH3T3 cells achieve a common growth arrest (G0) state by cell-specific strategies that involve the induction of different C/EBP isoforms.

3T3 Cells↗
PubMed1997

Highly selective iodide poly(vinyl chloride) membrane electrode based on a nickel(II) tetraazaannulene macrocyclic complex.

A PVC membrane electrode based on a nickel(II) tetraazaannulene macrocyclic complex as the carrier is described. The electrode exhibits an anti-Hofmeister selectivity sequence with a preference for iodide at pH 3.0-4.0. It has a linear response to iodide from 8.0 x 10(-6) to 1 x 10(-1) mol dm-3 with a slope of -54.7 +/- 0.2 mV per decade (20 degrees C), a satisfactory reproducibility and a rapid response time. The pH dependence of the potential response is discussed. The response mechanism of the electrode was investigated by ac impedance, quartz crystal microbalance and spectroscopic techniques. The electrode can be used for the determination of iodide in drug preparations.

Heterocyclic Compounds↗
PubMed1997

[Value of nasopharyngofiberoscope, spectrography and computer in diagnosis and treatment of pathologic speech after cleft palate operation].

The speech of 45 cases with velopharyngeal incompetence (VPI) were evaluated by combining application of nasopharyngofiberoscope (NPF) and computer-spectrographic analysis system (CSAS) after cleft palate operation and conservative speech therapy with using cleft palate obturators. The results showed: Improving rate of velopharyngeal incompetence (IRVPI) was close to 33.33% after 2.5-3 years therapy. The spectrographic analysis showed a clearer, and darken frequency band, normal resonance peaks (F2,F3) and seldom appearance of negative value of voice origination time (VOT). The above indicated that patients had achieved adequate velopharyngeal competence (VPC) and good speech habit. It has important significances and greatly improve speech therapy level to apply NPF and CSAS to analysing pathologic speech and evaluating therapic effect.

Adolescent↗
PubMed1997

Investigation of aortic CYP3A bioactivation of nitroglycerin in vivo.

Nitroglycerin (GTN) has been used to treat heart disease for many years. It is generally believed that GTN is a prodrug; however, the mechanism for GTN bioactivation remains unknown. Recent studies, using hepatic microsomes, have suggested the involvement of cytochrome P450 3A (CYP3A) in GTN biotransformation. Here, we used an animal model to test the hypothesis that aortic CYP3A plays a role in the bioactivation of GTN in vivo. Ketoconazole (KCZ), a potent CYP3A inhibitor, was given to rats (50 mg/kg i.p.) 1 hr before a bolus dose of GTN (2 mg/rat i.v.). KCZ decreased GTN-induced cGMP (cyclic guanosine monophosphate) levels by 20 to 30% (P < .05), without affecting basal or S-nitroso, N-acetyl penicillamine-induced levels of cGMP. When rats received dexamethasone (DEX, 30 mg/kg, 4 days i.p.), a strong CYP3A inducer, they exhibited a significant (approximately 50%) higher cGMP response to GTN than the control group. When rats received the combination treatment of both DEX and KCZ, they responded to GTN to the same extent as control rats. Although the effect of KCZ on aortic CYP3A activity cannot be detected (activity in control rats is below the detection limit), KCZ markedly inhibited CYP3A activity in rat livers (2.02 +/- 0.04 vs. 0.31 +/- 0.04 nmol/mg prot/min, P < .05, in control vs. KCZ-treated rats, respectively) and in DEX pretreated rat aorta (0.145 +/- 0.036 vs. 0.042 +/- 0.037 nmol/mg prot/min, P < .05, in rats treated with DEX alone vs. rats treated with both DEX and KCZ, respectively). KCZ did not elicit an effect on aortic glutathione S-transferases, another major metabolic enzyme responsible for GTN biotransformation. DEX enhanced the aortic GST mu activity by 3-fold. However, the activity of GST in aorta did not correlate with the cGMP response to GTN. In conclusion, our results demonstrate that CYP3A activity in aorta is correlated with GTN bioactivation in vivo, but the contribution of this enzyme to overall GTN bioactivation is limited.

Animals↗
PubMed1997

tRNA-dependent amino acid transformations.

Aminoacyl-tRNAs are either synthesized directly by aminoacyl-tRNA synthetases or indirectly by tRNA-dependent transformation of mischarged tRNAs. The enzymes which participate in the indirect routes may be interesting targets in the development of novel therapeutic compounds. We have purified one such enzyme, Glu-tRNA(Gln) amidotransferase from Bacillus subtilis, to homogeneity and present the initial biochemical characterization data.

Bacillus subtilis↗
PubMed1996

Immunoglobulin G3 blocking antibodies to the fungal pathogen Cryptococcus neoformans.

Vaccination and infection can elicit protective and nonprotective antibodies to the fungus Cryptococcus neoformans in mice. The effect of nonprotective antibodies on host defense is unknown. In this study we used mixtures of protective and nonprotective monoclonal antibodies (mAbs) to determine if nonprotective mAbs blocked the activity of the protective mAbs. Antibody isotype and epitope specificity are important in determining the ability to prolong survival in mice given a lethal C. neoformans infection. Three different nonprotective immunoglobulin (Ig) G23 mAbs to cryptococcal capsular polysaccharide were used to study the interaction between the IgG3 isotype and protective IgG1 and IgG2a mAbs in murine cryptococcal infection. One IgG3 mAb reduced the protective efficacy of an IgG1 with identical epitope specificity. A second IgG3 mAb with different epitope specificity also reduced the protection provided by the IgG1 mAb. The protective efficacy of an IgG2a mAb was also dramatically decreased by still another IgG3 mAb. To our knowledge this is the first report of blocking antibodies to a fungal pathogen. The results have important implications for the development of vaccines and passive antibody therapy against C. neoformans.

Animals↗
PubMed1995

Isotype switching from IgG3 to IgG1 converts a nonprotective murine antibody to Cryptococcus neoformans into a protective antibody.

Passively administered mAbs to Cryptococcus neoformans capsular polysaccharide can alter the course of infection in mouse models. In preliminary studies of passive Ab efficacy, most IgM, IgA, and IgG1 mAbs were protective, but the few IgG3 mAbs tested did not confer significant protection. Because IgG3 is effective in pneumococcal infections, this phenomenon was examined more rigorously by generating an IgG1 switch variant from the non-protective IgG3 mAb 3E5 and comparing its protective efficacy in a murine model of i.v. infection by using strains of both the A and D serotypes. The 3E5 IgG3 mAb did not prolong survival or reduce organ fungal burden. Rather, the IgG3 decreased survival relative to controls. In contrast, the IgG1 switch variant of 3E5 significantly prolonged survival, reduced organ colony-forming units, and reduced serum polysaccharide Ag level in infected mice. The results establish that isotype is important for Ab efficacy against C. neoformans.

Animals↗
PubMed1994

Simultaneous expression of kappa and lambda light chains in a murine IgG3 anti-Cryptococcus neoformans hybridoma cell line.

Allelic exclusion normally results in the expression of only one light and one heavy chain gene. However, some hybridomas have been reported to express two different heavy chain genes. Here we report that the IgG3 hybridoma 4H3.C8B expresses both kappa and lambda light chains. 4H3.C8B was originally recovered by screening for antibody binding to Cryptococcus neoformans polysaccharide antigen and characterized as gamma 3 lambda. The gamma 3 lambda but not the gamma 3 kappa binds to polysaccharide antigen. Some of the antibody molecules were heterodimers composed of both lambda and kappa. IgG1 and IgG2b isotype switch variants were identified and isolated by the technique of sib selection, using the ELISA spot assay. Like the parent IgG3 line, the switch variants continued to express both kappa and lambda light chains but only the lambda-containing antibodies bound to the antigen. Our experience suggests that hybridomas recovered by assays that are antigen dependent should also be tested for the expression of other isotypes and light chains in a non-antigen-binding immunoassay.

Alleles↗
PubMed1994

Management of injuries caused by Cryptococcus neoformans--contaminated needles.

This report describes four skin-puncture accidents with needles that were heavily contaminated with Cryptococcus neoformans. In one accident, delayed administration of antifungal drugs resulted in a granuloma of the finger. In the other three accidents, no skin infection followed immediate prophylaxis with oral fluconazole. Our experience suggests that early therapy with fluconazole is a reasonable means of managing skin injuries caused by instruments contaminated with viable C. neoformans.

Accidents↗
PubMed1993

Changes in keratometric astigmatism after suture removal more than one year after penetrating keratoplasty.

BACKGROUND/PURPOSE: Selective removal of interrupted sutures and adjustment of a running suture can minimize astigmatism after penetrating keratoplasty, but the long-term effects of early suture manipulations remain largely unknown. The authors tested the hypothesis that the cornea becomes "fixed" more than 1 year after keratoplasty so that desirable refractive results will remain when all sutures are eventually removed. METHODS: The authors reviewed retrospectively the changes in astigmatism that occurred when all remaining sutures were removed from 162 eyes 1 to 6 years after penetrating keratoplasty. Single-running sutures were used in 130 eyes, double-running sutures in 20 eyes, and a combination of interrupted and running sutures in 12 eyes. RESULTS: Removal of single-running sutures caused an average decrease in astigmatism of 0.52 diopters (D) from 6.10 +/- 4.41 D to 5.57 +/- 3.14 D. However, the astigmatism in 62% of eyes changed 2 or more D (range, 11.94 to -17.87 D), and the range changed more than 20 degrees in 55% of eyes. The average vectorial change was 6.5 +/- 4.3 D (range, 0.59 to 19.8 D). There was no decrease in the amount of astigmatic change with increasing time between surgery and suture removal. Graft size and diagnosis had no effect on the amount of astigmatic change. Astigmatic errors became stable, with less than 1 D of change between successive examinations within 6 months after suture removal. Similar results were obtained for eyes with double-running and interrupted-running sutures. CONCLUSIONS: Corneal astigmatism may change unpredictably and by large amounts when all remaining sutures are removed 1 to 6 years after penetrating keratoplasty.

Astigmatism↗
PubMed1993

Detection of bcl-2/JH rearrangement in follicular and diffuse lymphoma: concordant results of peripheral blood and bone marrow analysis at diagnosis.

The capacity to detect t(14;18) breakpoints in non-Hodgkin's lymphoma (NHL) peripheral blood and bone marrow was studied by DNA PCR. We studied 33 patients with follicular lymphoma (FL) (Working Formulation subtypes B, C, D) and 38 patients with intermediate-grade NHL (subtypes F, G). In the FL subgroup, 86% of the morphologically-positive bone marrow patients had amplifiable t(14;18) breakpoints by PCR. Remarkably, of 19 FL patients with 'negative' bone marrows, 11 (58%) were PCR-positive. In addition, half of the early clinical stage patients (I and II) had detectable breakpoints in their bone marrow DNA. Samples from NHL patients with intermediate-grade disease exhibit the same phenomena but at a considerably lower frequency. Paired peripheral blood and bone marrow samples were available at diagnosis in a subset of 56 patients. The concordance between bone marrow and peripheral blood PCR findings was high, with peripheral blood of 55/56 showing the same PCR results as the corresponding bone marrow.

Base Sequence↗
PubMed1993

Controlling unwanted sources of threshold change in disability glare studies: a prototype apparatus and procedure.

One of the main purposes of cataract surgery is to reduce the debilitating effects of light scatter by the lens. An important effect of this intraocular forward scatter is to produce a veiling retinal illuminance from a glare source. The retinal contrast of the stimulus is thus reduced, and a quantifiable "disability glare" effect may be measured. A complication is introduced by the fact that intraocular scatter arises from other sources in addition to the lens. All present tests of glare disability fail to eliminate or control for these factors, nor do they control for the light adaptation effect of the glare source. The effects of lens removal may not be predicted accurately by such tests, and patients may report little improvement in visual function after surgery. The goal of this research is to provide the background for developing a method of measuring disability glare due only to light scatter in the lens. Thirty-seven patients with mild to moderate cortical cataracts served as subjects. A disability glare effect (DG) was measured with a Maxwellian-view system that eliminates or controls scatter from the iris, sclera, and retina, and which controls for light-adaptation effects from the glare source. DG with this method showed a significant correlation with objective measures of lens light back scatter. Suggestions were made for improvements in the apparatus and procedures for future clinical studies.

Aged↗
PubMed1992

Reduction of foveal desensitization with blurred backgrounds.

Photopic spatial desensitization and sensitization (Westheimer) functions were measured with sharp edged and blurred edged backgrounds. Data show that for 6-min backgrounds, desensitization is reduced for test flashes presented against blurred backgrounds compared to test flashes presented against backgrounds with sharp edges. We suggest that the transients from edges of retinal images, caused by high frequency fixational eye movements, contribute to the mechanisms of spatial desensitization and sensitization; the effect of transients is reduced by blurring the backgrounds.

Adaptation, Ocular↗
PubMed1992

What is the utility of the psychophysical 'light scattering factor'?

It has been suggested by Sjöstrand and his colleagues that an index of scatter by the ocular media may be derived from contrast sensitivity measured with and without a glare source. This index was tested under different conditions of stimulus luminance and found not to be constant and thus to not reflect a property of the media.

Adult↗
PubMed1991

A new method for the rapid identification of genes encoding restriction and modification enzymes.

We have constructed derivatives of Escherichia coli that can be used for the rapid identification of recombinant plasmids encoding DNA restriction enzymes and methyltransferases. The induction of the DNA-damage inducible SOS response by the Mcr and Mrr systems, in the presence of methylated DNA, is used to select plasmids encoding DNA methyltransferases. The strains of E. coli that we have constructed are temperature-sensitive for the Mcr and Mrr systems and have been further modified to include a lacZ gene fused to the damage-inducible dinD locus of E. coli. The detection of recombinant plasmids encoding DNA methyltransferases and restriction enzymes is a simple, one step procedure that is based on the induction at the restrictive temperature of the lacZ gene. Transformants encoding DNA methyltransferase genes are detected on LB agar plates supplemented with X-gal as blue colonies. Using this method, we have cloned a variety of DNA methyltransferase genes from diverse species such as Neisseria, Haemophilus, Treponema, Pseudomonas, Xanthomonas and Saccharopolyspora.

Cloning, Molecular↗