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41.
Coregulation of beta-galactoside uptake and hydrolysis by the hyperthermophilic bacterium Thermotoga neapolitana 下载免费PDF全文
Regulation of the beta-galactoside transport system in response to growth substrates in the extremely thermophilic anaerobic bacterium Thermotoga neapolitana was studied with the nonmetabolizable analog methyl-beta-D-thiogalactopyranoside (TMG) as the transport substrate. T. neapolitana cells grown on galactose or lactose accumulated TMG against a concentration gradient in an intracellular free sugar pool that was exchangeable with external galactose or lactose and showed induced levels of beta-galactosidase. Cells grown on glucose, maltose, or galactose plus glucose showed no capacity to accumulate TMG, though these cells carried out active transport of the nonmetabolizable glucose analog 2-deoxy-D-glucose. Glucose neither inhibited TMG uptake nor caused efflux of preaccumulated TMG; rather, glucose promoted TMG uptake by supplying metabolic energy. These data show that beta-D-galactosides are taken up by T. neapolitana via an active transport system that can be induced by galactose or lactose and repressed by glucose but which is not inhibited by glucose. Thus, the phenomenon of catabolite repression is present in T. neapolitana with respect to systems catalyzing both the transport and hydrolysis of beta-D-galactosides, but inducer exclusion and inducer expulsion, mechanisms that regulate permease activity, are not present. Regulation is manifest at the level of synthesis of the beta-galactoside transport system but not in the activity of the system. 相似文献
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Hassan Anwarul KM; Moriya Shigeki; Baumann Paul; Yoshikawa Hiroshi; Ogasawara Naotake 《DNA research》1996,3(6):415-419
Buchnera aphidicola is an intracellular prokaryote (endosymbiont)that lives in the body cavity of the aphid. Phylogenetic studiesindicated that it is closely related to Escherichia coli andmembers of Enterobacteria. The gene order of the region containingthe dnaA gene is well conserved in many bacteria. Seven genesof the endosymbiont of the aphid Schizaphis graminum, gyrB,dnaN, dnaA, rpmH, rnpA, yidD, and 60K, were found to be homologousin sequence and relative location to those of E. coli. We havefurther sequenced the region downstream of the 60K gene to elucidatethe boundary of the conserved region, and found that one moregene, thdF , is conserved. The comparison of gene organizationsof the dnaA region of the related bacteria supported the closephylogenetic relationship of B. aphidicola to E. coli. In addition,we have identified groES and groEL genesnext to the thdF gene.GroEL protein was reported to be expressed at an elevated levelin the endosymbionts of aphids, and is considered to play animportant role in their association with the aphid host. Comparisonof the structure of the groE operon with that of the endosymbiontof the aphid Acyrthosiphon pisum revealed the conservation ofa sequence resembling the E. coli consensus heat shock promoter,and this sequence may be responsible for the high expressionof the groEL gene in aphid endosymbionts. 相似文献
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BACKGROUND: By 2016, the proportion of Canadians older than 65 years of age will increase to 16%, and there will be an increase in the absolute number of cases of cardiovascular disease in older Canadians. The Canadian Heart Health Surveys database provides information about this population upon which health policy related to cardiovascular disease can be based. This paper presents for the first time population-based data on the risk factors for cardiovascular disease in older Canadians. METHODS: Canadians from all 10 provinces participated in surveys of cardiovascular risk factors; health insurance registries were used as sampling frames. In each province, probability samples of 2200 adults 18 to 74 years old not living in institutions, on reserves or in military camps were asked to participate in interviews and to undergo testing at clinics for major risk factors for cardiovascular disease. RESULTS: A total of 2739 men (response rate 70%) and 2617 women (response rate 66%) aged 55 to 74 years participated in the survey and also provided follow-up clinical measurements at the clinic. Overall, 52% of participants were hypertensive, 26% had isolated systolic hypertension, and 30% had a total blood cholesterol level of 6.2 mmol/L or greater. Rates of current smoking were lower in women than men (17% v. 22%). Overall, 87% of men and 78% of women who were current smokers smoked at least 10 cigarettes per day. Only slightly more than half of participants exercised at least once a week for at least 15 minutes, and almost half had a body mass index of 27 or greater. In only 4% was no major risk factor for cardiovascular disease detected. INTERPRETATION: Significant numbers of older Canadians have one or more major risk factors for cardiovascular disease. Many of these risk factors are amenable to modification. 相似文献
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There are two approaches to the discovery of enzyme mimics, that is identifying molecules that are able to bind substrate(s) and then catalyze reactions. The first approach, often inspired by enzymes themselves, utilises chemical knowledge and experience to design the catalyst. The other approach is to create a library and select the best host of a transition state analogue of the required reaction. 相似文献
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Context
Medical educational reform includes enhancing role modelling of clinical teachers. This requires faculty being aware of their role model status and performance. We developed the System for Evaluation of Teaching Qualities (SETQ) to generate individualized feedback on previously defined teaching qualities and role model status for faculty in (non) academic hospitals.Objectives
(i) To examine whether teaching qualities of faculty were associated with their being seen as a specialist role model by residents, and (ii) to investigate whether those associations differed across residency years and specialties.Methods & Materials
Cross-sectional questionnaire survey amongst 549 Residents of 36 teaching programs in 15 hospitals in the Netherlands. The main outcome measure was faculty being seen as specialist role models by residents. Statistical analyses included (i) Pearson''s correlation coefficients and (ii) multivariable logistic generalized estimating equations to assess the (adjusted) associations between each of five teaching qualities and ‘being seen as a role model’.Results
407 residents completed a total of 4123 evaluations of 662 faculty. All teaching qualities were positively correlated with ‘being seen as a role model’ with correlation coefficients ranging from 0.49 for ‘evaluation of residents’ to 0.64 for ‘learning climate’ (P<0.001). Faculty most likely to be seen as good role models were those rated highly on ‘feedback’ (odds ratio 2.91, 95% CI: 2.41–3.51), ‘a professional attitude towards residents’ (OR 2.70, 95% CI: 2.34–3.10) and ‘creating a positive learning climate’ (OR 2.45, 95% CI: 1.97–3.04). Results did not seem to vary much across residency years. The relative strength of associations between teaching qualities and being seen as a role model were more distinct when comparing specialties.Conclusions
Good clinical educators are more likely to be seen as specialist role models for most residents. 相似文献49.
Susanna KP Lau Rachel YY Fan Gilman KM Wong Jade LL Teng Kong-Hung Sze Herman Tse Kwok-Yung Yuen Patrick CY Woo 《Cell & Bioscience》2011,1(1):1-17
Background
Laribacter hongkongensis is a Gram-negative, sea gull-shaped rod associated with community-acquired gastroenteritis. The bacterium has been found in diverse freshwater environments including fish, frogs and drinking water reservoirs. Using the complete genome sequence data of L. hongkongensis, we performed a comprehensive analysis of putative transport-related genes and genes related to chemotaxis, motility and quorum sensing, which may help the bacterium adapt to the changing environments and combat harmful substances.Results
A genome-wide analysis using Transport Classification Database TCDB, similarity and keyword searches revealed the presence of a large diversity of transporters (n = 457) and genes related to chemotaxis (n = 52) and flagellar biosynthesis (n = 40) in the L. hongkongensis genome. The transporters included those from all seven major transporter categories, which may allow the uptake of essential nutrients or ions, and extrusion of metabolic end products and hazardous substances. L. hongkongensis is unique among closely related members of Neisseriaceae family in possessing higher number of proteins related to transport of ammonium, urea and dicarboxylate, which may reflect the importance of nitrogen and dicarboxylate metabolism in this assacharolytic bacterium. Structural modeling of two C4-dicarboxylate transporters showed that they possessed similar structures to the determined structures of other DctP-TRAP transporters, with one having an unusual disulfide bond. Diverse mechanisms for iron transport, including hemin transporters for iron acquisition from host proteins, were also identified. In addition to the chemotaxis and flagella-related genes, the L. hongkongensis genome also contained two copies of qseB/qseC homologues of the AI-3 quorum sensing system.Conclusions
The large number of diverse transporters and genes involved in chemotaxis, motility and quorum sensing suggested that the bacterium may utilize a complex system to adapt to different environments. Structural modeling will provide useful insights on the transporters in L. hongkongensis. 相似文献50.
Singaram?Gopalakrishnan Napo?KM?Cheung Bill?WP?Yip Doris?WT?AuEmail author 《Frontiers in zoology》2013,10(1):78