[Identification of high-pathogenicity island-harboring Escherichia coli from children with diarrhea disease]

OBJECTIVE

To investigate the etiological status of high-pathogenicity island-harboring Escherichia coli (HPIEC) in diarrhea diseases among children.

METHODS

Escherichia coli was Isolated and identified from the stool specimens of 1,032 children with diarrhea diseases by culturing, serotyping, PCR, and colony hybridization.

RESULTS

652 strains of E. coli were isolated from the 1,032 stool specimens and confirmed by colony hybridization out of which 225 were identified as diarrheagenic E. coli, including 20 EPEC, 81 ETEC, 47 SLTEC, 74 ESIEC, and 3 EIEC strans. 112 (17.2%) irp2 virulent gene positive E. coli strains were detected from the 652 strains, out of which 24 were from the 74 ESIEC strans and 17 from the 47 SLTEC stranis. The typical clinical symptoms of diarrhea caused by HPI-haboring E. coli included anorexia (87.5%), abdominal pain (58.0%), diarrhea (75.9%, over 6 episodes, mostly of mucous stool a day, 75.9%), and fever (50.9%).

CONCLUSION

High-pathogenicity island-harboring E. coli is one of the important pathogens of diarrhea diseases in children.

[Effect of alcohol extract of Cornus officinalis Sieb. et Zucc on GLUT4 expression in skeletal muscle in type 2 (non-insulin-dependent) diabetic mellitus rats]

OBJECTIVE

Based on its effects of decreasing postprandial plasma glucose and increasing insulin level in non-insulin-dependent diabetic mellitus (NIDDM) rats, we studied the effects of Alcohol extract of Cornus officinalis Sieb. et Zucc on the GLUT4 expression in NIDDM model rats.

METHOD

The rat model of NIDDM was made. The animals were divided into three groups(six for each group): group I: control; group II: NIDDM model; group III: NIDDM model + Cornus officinalis Sieb. et Zucc. The drug was given orally to animals one time a day, uninterrupted for a month. The GLUT4 mRNA and its protein expression in skeletal muscle were observed with Northern blot and Western blot method, respectively.

RESULT

The GLUT4 mRNA expression in skeletal muscle was decreased remarkably in NIDDM rats (P < 0.01, compared to control group). Alcohol extract of Cornus officinalis Sieb. et Zucc increased GLUT4 mRNA expression in NIDDM rats(P < 0.01), compared to NIDDM model group). The result of GLUT4 protein expression was similar to GLUT4 mRNA expression.

CONCLUSION

This experiment demonstrated that alcohol extract of Cornus officinalis Sieb. et Zucc can increase GLUT4 mRNA and its protein expression in NIDDM rats through promoting proliferation of islet and increasing postprandial secretion of insulin and therefore accelerate glucose transport.

Simultaneous near-infrared diffusive light and ultrasound imaging

We have constructed a near-real-time combined imager suitable for simultaneous ultrasound and near-infrared diffusive light imaging and coregistration. The imager consists of a combined hand-held probe and the associated electronics for data acquisition. A two-dimensional ultrasound array is deployed at the center of the combined probe, and 12 dual-wavelength laser source fibers (780 and 830 nm) and 8 optical detector fibers are deployed at the periphery. We have experimentally evaluated the effects of missing optical sources in the middle of the combined probe on the accuracy of the reconstructed optical absorption coefficient and assessed the improvements of a reconstructed absorption coefficient with the guidance of the coregistered ultrasound. The results have shown that, when the central ultrasound array area is in the neighborhood of 2 cm x 2 cm, which corresponds to the size of most commercial ultrasound transducers, the optical imaging is not affected. The results have also shown that the iterative inversion algorithm converges quickly with the guidance of a priori three-dimensional target distribution, and only one iteration is needed to reconstruct an accurate optical absorption coefficient.

A novel pathway for lipid biosynthesis: the direct acylation of glycerol

The acylation of glycerol-3-phosphate by acyl-CoA is regarded as the first committed step for the synthesis of the lipoidal moiety in glycerolipids. The direct acylation of glycerol in mammalian tissues has not been demonstrated. In this study, lipid biosynthesis in myoblasts and hepatocytes was reassessed by conducting pulse-chase experiments with [1,3-(3)H]glycerol. The results demonstrated that a portion of labeled glycerol was directly acylated to form monoacylglycerol and, subsequently, diacylglycerol and triacylglycerol. The direct acylation of glycerol became more prominent when the glycerol-3-phosphate pathway was attenuated or when exogenous glycerol levels became elevated. Glycerol:acyl-CoA acyltransferase activity, which is responsible for the direct acylation of glycerol, was detected in the microsomal fraction of heart, liver, kidney, skeletal muscle, and brain tissues. The enzyme from pig heart microsomes displayed optimal activity at pH 6.0 and the preference for arachidonyl-CoA as the acyl donor. The apparent K(m) values for glycerol and arachidonyl-CoA were 1.1 mM and 0.17 mM, respectively. The present study demonstrates the existence of a novel lipid biosynthetic pathway that may be important during hyperglycerolemia produced in diabetes or other pathological conditions.

Influenza virus infection induces metallothionein gene expression in the mouse liver and lung by overlapping but distinct molecular mechanisms

Metallothionein I (MT-I) and MT-II have been implicated in the protection of cells against reactive oxygen species (ROS), heavy metals, and a variety of pathological and environmental stressors. Here, we show a robust increase in MT-I/MT-II mRNA level and MT proteins in the livers and lungs of C57BL/6 mice exposed to the influenza A/PR8 virus that infects the upper respiratory tract and lungs. Interleukin-6 (IL-6) had a pronounced effect on the induction of these genes in the liver but not the lung. Treatment of the animals with RU-486, a glucocorticoid receptor antagonist, inhibited induction of MT-I/MT-II in both liver and lung, revealing a direct role of glucocorticoid that is increased upon infection in this induction process. In vivo genomic footprinting (IVGF) analysis demonstrated involvement of almost all metal response elements, major late transcription factor/antioxidant response element (MLTF/ARE), the STAT3 binding site on the MT-I upstream promoter, and the glucocorticoid responsive element (GRE1), located upstream of the MT-II gene, in the induction process in the liver and lung. In the lung, inducible footprinting was also identified at a unique gamma interferon (IFN-gamma) response element (gamma-IRE) and at Sp1 sites. The mobility shift analysis showed activation of STAT3 and the glucocorticoid receptor in the liver and lung nuclear extracts, which was consistent with the IVGF data. Analysis of the newly synthesized mRNA for cytokines in the infected lung by real-time PCR showed a robust increase in the levels of IL-10 and IFN-gamma mRNA that can activate STAT3 and STAT1, respectively. A STAT1-containing complex that binds to the gamma-IRE in vitro was activated in the infected lung. No major change in MLTF/ARE DNA binding activity in the liver and lung occurred after infection. These results have demonstrated that MT-I and MT-II can be induced robustly in the liver and lung following experimental influenza virus infection by overlapping but distinct molecular mechanisms.

Organic/inorganic hybrid composites from cubic silsesquioxanes

A new class of epoxy nanocomposites with completely defined organic/inorganic phases was prepared by reacting octakis(glycidyldimethylsiloxy)octasilsesquioxane [(glydicylMe(2)SiOSiO(1.5))(8)] (OG) with diaminodiphenylmethane (DDM) at various compositional ratios. The effects of reaction curing conditions on nanostructural organization and mechanical properties were explored. A commercial epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) was used as a reference material throughout these studies. FTIR was used to follow the curing process and to demonstrate that the silsesquioxane structure is preserved during processing. OG/DDM composites possess comparable tensile moduli (E) and fracture toughness (K(IC)) to, and better thermal stabilities than, DGEBA/DDM cured under similar conditions. Dynamic mechanical analysis and model reaction studies suggest that the maximum cross-link density is obtained at N = 0.5 (NH(2):epoxy groups = 0.5) whereas the mechanical properties are maximized at N = 1.0. Digestion of the inorganic core with HF followed by GPC analysis of the resulting organic tether fragments when combined with the model reaction studies confirms that, at N = 0.5, each organic tether connects four cubes, while, at N = 1.0, linear tethers connecting two cubes dominate the network structure. Thus, well-defined nanocomposites with controlled variation of the organic tether architecture can be made and their properties assessed.

The 7SK small nuclear RNA inhibits the CDK9/cyclin T1 kinase to control transcription

The human positive transcription elongation factor P-TEFb, consisting of a CDK9/cyclin T1 heterodimer, functions as both a general and an HIV-1 Tat-specific transcription factor. P-TEFb activates transcription by phosphorylating RNA polymerase (Pol) II, leading to the formation of processive elongation complexes. As a Tat cofactor, P-TEFb stimulates HIV-1 transcription by interacting with Tat and the transactivating responsive (TAR) RNA structure located at the 5' end of the nascent viral transcript. Here we identified 7SK, an abundant and evolutionarily conserved small nuclear RNA (snRNA) of unknown function, as a specific P-TEFb-associated factor. 7SK inhibits general and HIV-1 Tat-specific transcriptional activities of P-TEFb in vivo and in vitro by inhibiting the kinase activity of CDK9 and preventing recruitment of P-TEFb to the HIV-1 promoter. 7SK is efficiently dissociated from P-TEFb by treatment of cells with ultraviolet irradiation and actinomycin D. As these two agents have been shown to significantly enhance HIV-1 transcription and phosphorylation of Pol II (refs 6,7,8), our data provide a mechanistic explanation for their stimulatory effects. The 7SK/P-TEFb interaction may serve as a principal control point for the induction of cellular and HIV-1 viral gene expression during stress-related responses. Our studies demonstrate the involvement of an snRNA in controlling the activity of a Cdk-cyclin kinase.

Cysteine-directed cross-linking localizes regions of the human erythrocyte anion-exchange protein (AE1) relative to the dimeric interface

The human erythrocyte anion-exchanger isoform 1 (AE1) is a dimeric membrane protein that exchanges chloride for bicarbonate across the erythrocyte plasma membrane. Crystallographic studies suggest that the transmembrane anion channel lies at the interface between the two monomers, whereas kinetic analysis provides evidence that each monomer contains an anion channel. We have studied the structure-function relationship of residues at the dimeric interface of AE1 by cysteine-directed cross-linking. Single cysteine mutations were introduced in 16 positions of putative loop regions throughout AE1. The ability of these residues to be chemically cross-linked to their partner within the dimeric protein complex was assessed by mobility of the protein on immunoblots. Introduced cysteine residues in extracellular loops (ECs) 1-4 and intracellular loop 1 formed disulphide cross-linked dimers. Treatment with homobifunctional maleimide cross-linkers of different lengths (6, 10 and 16 A; 1 A identical with 0.1 nm) also cross-linked AE1 with introduced cysteines in EC5 and close to the start of transmembrane segment (TM) 1. On the basis of these data, tentative positional constraints of TMs 1-4 and 6 relative to the dimeric interface are proposed. Neither disulphide- nor maleimide-mediated cross-linking perturbed AE1 transport function, suggesting that loop-loop contacts across the dimeric interface are not primarily responsible for allosteric interactions between monomers within the functional dimeric protein complex.

Dendritic cell-derived IL-12 is not required for the generation of cytotoxic, IFN-gamma-secreting, CD8(+) CTL in vivo

By using adoptive transfer of Ag-loaded bone marrow-derived dendritic cells (BMDC), we have established an in vivo model of CTL priming. Activation of CTL in these experiments required both CD4(+) T cells and CD154, demonstrating that this model reflects CD4(+) T cell-dependent dendritic cell (DC) licensing. Because IL-12 has been suggested to play an important role in CTL activation by DC, we examined the ability of BMDC to prime CTL in the complete absence of IL-12 using p40-deficient mice. We observed that the absence of IL-12 does not affect the phenotype or allostimulatory function of BMDC after in vitro maturation. Moreover, there was no difference in the ability of Ag-loaded DC to elicit CTL cytotoxicity, whether the Ag was delivered by virus infection or peptide pulsing. Equal frequencies of Ag-specific, IFN-gamma-secreting CD8(+) T cells developed in both wild-type and IL-12-deficient backgrounds. Finally, CTL generated in the IL-12-deficient environment were capable of protecting immunized mice against tumor challenge, demonstrating that these CTL were fully functional, despite the absence of IL-12 during the maturation process in vivo. These results indicate that IL-12 is not critical for the development of IFN-gamma secreting, CD8(+) T cells and that another mechanism must be used by licensed DC to prime and activate CTL.

[Correlation between nutrient levels of vitamin A and zinc and HOX C4 gene expression in mice embryos]

OBJECTIVE

Correlation between nutrient levels of vitamin A and zinc and HOX C4 (3.5) gene expression in mice embryos was studied.

METHODS

The Kunming female mice were divided three groups: deficient group (DG) fed with fodder deficient of vitamin A and zinc, replenished group (RG) fed with fodder deficient of vitamin A and zinc until the 7th day after conception and then fed with fodder rich in vitamin A and zinc, and normal group (NG), fed with normal fodder. After obvious symptoms of vitamin A and zinc deficiency appeared, the mice were mated. On the 12th day after conception, pregnant mice were killed and their levels of vitamin A and zinc were determined and the content of mRNA of HOX C4 (3.5) were determined for the embryos with situ hybridization.

RESULTS

The level of vitamin A was 0.44 mumol/L, 1.03 mumol/L and 1.40 mumol/L, respectively and that of zinc 124.3 mg/kg, 152.1 mg/kg and 193.8 mg/kg in DG, RG and NG, respectively. The mRNA of HOX C4 (3.5) gene expression in mouse embryos increased significantly in DG, RG and NG (P < 0.05).

CONCLUSIONS

Levels of vitamin A and zinc in the body of pregnant mice positively correlated significantly with their HOX C4 (3.5) gene expression, with coefficients of correlation of 0.78 to 0.99.

[Effect of zinc deficiency and zinc replenishment on HOX3.5 gene expression in mouse embryos]

The effect of zinc deficiency and zinc replenishment on HOX3.5 gene expression in mouse embryos was investigated. Sixty Kunming female mice (25-30 g) were divided into three groups: zinc-deficient groups (ZD), zinc-replenished group (ZR) and zinc normal controlled group (ZN). ZD mice fed with ZD diet (Zn 3.0 +/- 0.5 mg/kg), ZN mice fed with ZN diet (Zn 30 mg/kg), and ZR mice fed with ZD diet at first and then with ZN diet from the 7th day of pregnancy. After feeding different diet for 25 days, the mice were made to copulate (female: male = 2:1). At the 12th day of pregnancy, the mice were killed and the embryos were stored at -70 degrees C. The content of mRNA of HOX3.5 in the embryos were determined by in situ hybridization with digxigenin-labeled cDNA probes. The result showed that the expression on area density and L-density (average optical density) of Hox3.5 in ZD and ZR groups were decreased in comparing with those in ZN group (P < 0.05). It was suggested that the decreased HOX3.5 gene expression by zinc deficiency might influence the normal growth of mouse embryos, and this effect might occurr in the early stage of embryo development, which can not be prevented by replenishing zinc at the 7th day of pregnancy.

Activities of starch hydrolytic enzymes and sucrose-phosphate synthase in the stems of rice subjected to water stress during grain filling

To understand the effect of water stress on the remobilization of prestored carbon reserves, the changes in the activities of starch hydrolytic enzymes and sucrose-phosphate synthase (SPS) in the stems of rice (Oryza sativa L.) during grain filling were investigated. Two rice cultivars, showing high lodging-resistance and slow remobilization, were grown in the field and subjected to well-watered (WW, psi(soil)=0) and water-stressed (WS, psi(soil)=-0.05 MPa) treatments 9 d after anthesis (DAA) till maturity. Leaf water potentials of both cultivars markedly decreased during the day as a result of WS treatment, but completely recovered by early morning. WS treatment accelerated the reduction of starch in the stems, promoted the reallocation of prefixed (14)C from the stems to grains, shortened the grain filling period, and increased the grain filling rate. More soluble sugars including sucrose were accumulated in the stems under WS than under WW treatments. Both alpha- and beta-amylase activities were enhanced by the WS, with the former enhanced more than the latter, and were significantly correlated with the concentrations of soluble sugars in the stems. The other two possible starch-breaking enzymes, alpha-glucosidase and starch phosphorylase, showed no significant differences in the activities between the WW and WS treatments. Water stress also increased the SPS activity that is responsible for sucrose production. Both V(limit) and V(max), the activities of the enzyme at limiting and saturating substrate concentrations, were enhanced and the activation state (V(limit)/V(max)) was also increased as a result of the more significant enhancement of V(limit). The enhanced SPS activity was closely correlated with an increase of sucrose accumulation in the stems. The results suggest that the fast hydrolysis of starch and increased carbon remobilization were attributed to the enhanced alpha-amylase activity and the high activation state of SPS when the rice was subjected to water stress.

Observation and elimination of N-acetylation of oligonucleotides prepared using fast-deprotecting phosphoramidites and ultra-mild deprotection

Commercially available 'fast-deprotecting' phosphoramidites are useful for synthesizing oligonucleotides containing alkali-sensitive nucleotides. However, N-acetylated oligonucleotides were observed during solid-phase synthesis using 'fast-deprotecting' phosphoramidites in conjunction with K2CO3/MeOH ('ultra-mild') deprotection. Transamidation was localized at deoxyguanosine, which is protected as its isopropylphenoxyacetyl amide. Substitution of trimethylacetic anhydride for acetic anhydride and appropriate modification of the automated synthesis cycles eliminated this problem.

Analysis of a non-functional HNF-1alpha (TCF1) mutation in Japanese subjects with familial type 1 diabetes

Mutations in the transcription factor hepatocyte nuclear factor-1alpha (HNF-1alpha; gene symbol TCF1) cause maturity-onset diabetes of the young type 3 (MODY3), a form of diabetes mellitus characterized by autosomal dominant inheritance, early onset, and pancreatic beta-cell dysfunction. Recent genetic studies, however, also found mutations in patients diagnosed with idiopathic (non-autoimmune based) type 1 diabetes. We identified a novel frameshift mutation (142delG) in the TCF1 gene in a family with a strong family history of type 1 diabetes and examined the functional properties of the mutant HNF 1alpha. The expression of the mutant protein was not detected in COS-7 cells by Western blot analysis after transfection of the mutant cDNA. This is the first case of an unstable mutant HNF-1alpha protein. Reporter gene analysis indicated that the mutant HNF-1alpha had no transactivation activity in HeLa and MIN6 cells. Haploinsufficiency for HNF-1alpha may lead to severe forms of diabetes like type 1 diabetes.

Spot 14 gene deletion increases hepatic de novo lipogenesis

Previous studies have investigated the relationship between the Spot 14 gene and hepatic lipogenesis. Those studies found that the Spot 14 protein was induced when lipogenesis was induced and suggested that induction of the Spot 14 protein was required for induction of hepatic lipogenesis by thyroid hormone and dietary carbohydrate. Analysis of those findings led us to hypothesize that the Spot 14 gene is required for induced hepatic de novo lipogenesis in vivo. To test this hypothesis, we created an in vivo deletion of the Spot 14 gene in mice using gene-targeting technology. Southern blot analysis showed that the Spot 14 gene was disrupted. Northern blot analysis showed that this disruption ablated expression of intact hepatic Spot 14 mRNA. In contrast to our hypothesis, acute thyroid hormone administration led to comparable induction of hepatic lipogenic enzyme mRNAs between the wild-type and knockout mice. Furthermore, long-term treatment with both thyroid hormone and a diet promoting lipogenesis led to enhanced lipogenic enzyme activity and a greater rate of hepatic de novo lipogenesis in the knockout, compared with the wild-type, mice. Although these data indicate that the Spot 14 protein is not required for induced hepatic de novo lipogenesis, they also suggest that Spot 14 plays some role in this process. It is possible that alternative pathways that complement the loss of the Spot 14 protein are present, and in the absence of Spot 14, these alternative pathways overcompensate to produce an enhanced rate of induced lipogenesis.

Role of ovarian hormones in the pathogenesis of impaired detrusor contractility: evidence in ovariectomized rodents

PURPOSE

Although detrusor hyperactivity with impaired contractility is a common urodynamic finding in elderly subjects, to our knowledge its pathogenesis remains unknown. Biopsy studies indicate that subjects with detrusor hyperactivity and impaired contractility have ultrastructural evidence of dysjunction and degeneration patterns in isolated detrusor hyperactivity and impaired contractility, respectively. Based on the known cellular effects of estrogen we postulated that declines in ovarian hormone production may contribute to the pathogenesis of detrusor hyperactivity with impaired contractility.

MATERIALS AND METHODS

Mature 13 to 14-month-old female Fisher 344 rats were studied 4 months after bilateral ovariectomy or sham surgery. Detrusor structure was evaluated by electron microscopy and contractility was evaluated by muscle strip studies.

RESULTS

After bilateral ovariectomy detrusor smooth muscle decreased by 25% with a 12% decrease in the number of nucleated muscle profiles and degenerative changes in many axons. Muscle strips from bilaterally ovariectomized animals generated 40% to 50% less tension per strip in response to carbachol than strips of equal size from sham operated animals with no apparent change in muscarinic receptor affinity.

CONCLUSIONS

Bilateral ovariectomy resulted in many changes of the degeneration ultrastructural pattern but in none of the characteristic features of the dysjunction pattern. Our results indicate that the mature rodent detrusor and its innervation are sensitive to prolonged ovarian hormonal deficiency, contributing to impaired contractility in rodents. Future studies are required to establish whether estrogen has a role in the degeneration ultrastructural pattern or impaired contractility in humans.

Hormonal changes in the grains of rice subjected to water stress during grain filling

Lodging-resistant rice (Oryza sativa) cultivars usually show slow grain filling when nitrogen is applied in large amounts. This study investigated the possibility that a hormonal change may mediate the effect of water deficit that enhances whole plant senescence and speeds up grain filling. Two rice cultivars showing high lodging resistance and slow grain filling were field grown and applied with either normal or high amount nitrogen (HN) at heading. Well-watered and water-stressed (WS) treatments were imposed 9 days post anthesis to maturity. Results showed that WS increased partitioning of fixed (14)CO(2) into grains, accelerated the grain filling rate but shortened the grain filling period, whereas the HN did the opposite way. Cytokinin (zeatin + zeatin riboside) and indole-3-acetic acid contents in the grains transiently increased at early filling stage and WS treatments hastened their declines at the late grain filling stage. Gibberellins (GAs; GA(1) + GA(4)) in the grains were also high at early grain filling but HN enhanced, whereas WS substantially reduced, its accumulation. Opposite to GAs, abscisic acid (ABA) in the grains was low at early grain filling but WS remarkably enhanced its accumulation. The peak values of ABA were significantly correlated with the maximum grain filling rates (r = 0.92**, P < 0.01) and the partitioning of fixed (14)C into grains (r = 0.95**, P < 0.01). Exogenously applied ABA on pot-grown HN rice showed similar results as those by WS. Results suggest that an altered hormonal balance in rice grains by water stress during grain filling, especially a decrease in GAs and an increase in ABA, enhances the remobilization of prestored carbon to the grains and accelerates the grain filling rate.

Reduction of pacing output coupling capacitance for sensing the evoked response

Sensing of the intracardiac evoked response (ER) after a pacing stimulus has been used in implantable pacemakers for automatic verification of capture. Reliable detection of ER is hampered by large residual afterpotentials associated with pacing stimuli. This led to the development of various technological solutions, like the use of triphasic pacing pulses and low polarizing electrode systems. This study investigated the effect of reducing the coupling capacitance (CC) in the pacemaker output circuitry on the magnitude of afterpotential, and the ability to automate detection of ventricular evoked response. A CC of 2.2 microF and four different blanking and recharge time settings were clinically tested to evaluate its impact on sensing of the ventricular ER and pacing threshold. Using an automatic step-down threshold algorithm, 54 consecutive patients, aged 70 +/- 10 years with acutely (n = 27) or chronically (n = 27) implanted ventricular pacing leads were enrolled for measurement testing. Routine measurements, using a standard pacing system analyzer (PSA), were (mean +/- SD) impedance 569 +/- 155 omega, R wave amplitude baseline to peak 9.8 +/- 3.7 mV and threshold 0.9 +/- 0.7 V at 0.4-ms pulse width. This new capture verification scheme, based on a CC of 2.2 microF and recharge/blanking timing setting of 10/12 ms, was successful in 52 patients which is equivalent to a success rate of 96%. In a subgroup of 26 patients implanted with bipolar ventricular leads (10 chronic, 16 acute), data were collected in unipolar (UP) and bipolar (BP) pace/sense configurations. Also, ER signals were recorded with two different band-pass filters: a wider band (WB) of 6-250 Hz and a conventional narrow band (NB) of 20-100 Hz. WB sensing from UP lead configuration yielded statistically significant larger signal to artifact ratios (SAR) than the other settings (P < 0.01). A dedicated unipolar ER sensing configuration using a small output capacitor and a wider band-pass filter enables adequate automatic capture verification, without any restrictions on pacing lead models or pacing/sensing configurations.

Type I topoisomerase activity is required for proper chromosomal segregation in Escherichia coli

Type I DNA topoisomerases are ubiquitous enzymes involved in many aspects of DNA metabolism. Escherichia coli possesses two type I topoisomerase activities, DNA topoisomerase I (Topo I) and III (Topo III). The gene encoding Topo III (topB) can be deleted without affecting cell viability. Cells possessing a deletion of the gene encoding Topo I (topA) are only viable in the presence of an additional compensatory mutation. In the presence of compensatory mutations, Topo I deletion strains grow normally; however, if Topo III activity is repressed in these cells, they filament extensively and possess an abnormal nucleoid structure. These defects can be suppressed by the deletion of the recA gene, suggesting that these enzymes may be involved in RecA-mediated recombination and may specifically resolve recombination intermediates before partitioning.

Mdm2 mutant defective in binding p300 promotes ubiquitination but not degradation of p53: evidence for the role of p300 in integrating ubiquitination and proteolysis

Turnover of the p53 tumor suppressor protein is mediated by Mdm2 through the ubiquitin proteolysis pathway. p300, a co-activator for p53, also participates in this process by complexing with Mdm2. We now report that the mutant Mdm2, defective in p53 binding, does not promote p53 ubiquitination and degradation in vivo or inhibit p53 transcriptional activation. By contrast, the mutant Mdm2, defective in p300 binding, still retains its activity to promote p53 ubiquitination and to inhibit p53 transcriptional activation but fails in promoting p53 degradation. We also show that both wild-type Mdm2 and the mutant Mdm2, defective in p300 binding, can promote the ubiquitination of cancer-derived p53 mutants, but only wild-type Mdm2 can cause their degradation. Furthermore, adenoviral oncoprotein, 12S.E.1A, but not its deletion mutant that lacks p300 binding, was shown to decrease in vivo ubiquitination of mutant p53. Taken together, these results provide genetic evidence that p300 plays a pivotal role in the regulation of Mdm2-mediated p53 turnover by integrating the cellular ubiquitination and proteolytic processes.

A rare polyadenylation signal mutation of the FOXP3 gene (AAUAAA-->AAUGAA) leads to the IPEX syndrome

The mouse scurfy gene, Foxp3, and its human orthologue, FOXP3, which maps to Xp11.23-Xq13.3, were recently identified by positional cloning. Point mutations and microdeletions of the FOXP3 gene were found in the affected members of eight of nine families with IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked; OMIM 304930). We evaluated a pedigree with clinically typical IPEX in which mutations of the coding exons of FOXP3 were not detected. Our reevaluation of this pedigree identified an A-->G transition within the first polyadenylation signal (AAUAAA-->AAUGAA) after the stop codon. The next polyadenylation signal is not encountered for a further 5.1 kb. This transition was not detected in over 212 normal individuals (approximately 318 X chromosomes), excluding the possibility of a rare polymorphism. We suggest that this mutation is causal of IPEX in this family by a mechanism of nonspecific degradation of the FOXP3 gene message.

Design of near-infrared imaging probe with the assistance of ultrasound localization

A total of 364 optical source-detector pairs were deployed uniformly over a 9 cm x 9 cm probe area initially, and then the total pairs were reduced gradually to 60 in experimental and simulation studies. For each source-detector configuration, three-dimensional (3-D) images of a 1-cm-diameter absorber of different contrasts were reconstructed from the measurements made with a frequency-domain system. The results have shown that more than 160 source-detector pairs are needed to reconstruct the absorption coefficient to within 60% of the true value and appropriate spatial and contrast resolution. However, the error in target depth estimated from 3-D images was more than 1 cm in all source-detector configurations. With the a priori target depth information provided by ultrasound, the accuracy of the reconstructed absorption coefficient was improved by 15% and 30% on average, and the beam width was improved by 24% and 41% on average for high- and low-contrast cases, respectively. The speed of reconstruction was improved by ten times on average.

Nonclassical behavior in the capacitance of a nanojunction

The capacitance of a nanojunction formed by a scanning tunneling microscope (STM) tip and a two-dimensional gold cluster was measured through the single electron tunneling spectroscopy of a double-barrier tunnel junction. By decreasing the STM tip-cluster separation, it was observed that the capacitance first increases and then decreases at short separation. This characteristic clearly deviates from the classical behavior and provides evidence for potential quantum effects on the capacitance.