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51.
Evidence for two different gas vesicle proteins and genes in Halobacterium halobium. 总被引:6,自引:1,他引:5
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Most halobacteria produce gas vesicles (GV). The well-characterized species Halobacterium halobium and some GV+ revertants of GV- mutants of H. halobium produce large amounts of GV which have a spindlelike shape. Most other GV+ revertants of H. halobium GV- mutants and other recently characterized halobacterial wild-type strains possess GV with a cylindrical form. The number of intact particles in the latter isolates is only 10 to 30% of that of H. halobium. Analysis of GV envelope proteins (GVPs) by electrophoresis on phenol-acetic acid-urea gels showed that the GVP of the highly efficient GV-producing strains migrated faster than the GVP of the low-GV-producing strains. The relative molecular mass of the GVP was estimated to be 19 kilodaltons (kDa) for high-producing strains (GVP-A) and 20 kDa for low-producing strains (GVP-B). Amino acid sequence analysis of the first 40 amino acids of the N-terminal parts of GVP-A and GVP-B indicated that the two proteins differed in two defined positions. GVP-B, in relation to GVP-A, had Gly-7 and Val-28 always replaced by Ser-7 and Ile-28, respectively. These data suggest that at least two different gvp genes exist in H. halobium NRL. This was directly demonstrated by hybridization experiments with gvp-specific DNA probes. A fragment of plasmid pHH1 and a chromosomal fragment of H. halobium hybridized to the probes. Only a chromosomal fragment hybridized to the same gyp probes when both chromosomal and plasmid DNAs from the low-GV-producing halobacterial wild-type strains SB3 and GN101 were examined. These findings support the assumption that GVP-A is expressed by a pHH1-associated gvp gene and GVP-B by a chromosomal gvp gene. 相似文献
52.
Homogeneous phosphoribulokinase (PRK; ATP: d-ribulose-5-phosphate 1-phosphotransferase, EC 2.7.1.19) was isolated from wheat leaves with a specific activity of 15 kat mg-1 protein. The purification included ammonium sulfate cuts, isoelectric precipitation, and hydrophobic and affinity chromatography on pentylagarose and Blue Sepharose CL 6B, respectively. Gel filtration of the purified enzyme yielded a 83000 Da protein. Subunits of about 42000 Da were estimated from sodium dodecyl sulfate-polyacrylamide gels. Wheat leaf PRK was stable for at least four weeks when stored at 4°C. Saturation curves for ribulose 5-phosphate (Ru5P) and ATP followed Michaelis-Menten kinetics (K
m values: K
m Ru5P=50–80 M; K
m ATP=70 M). The saturation curve for MgCl2 was sigmoidal (half-maximal velocity <0.5 mM). The affinity for Ru5P, ATP and Mg2+ was not affected by pH changes comparable to pH shifts in the stroma. In contrast to chloroplast fructose-bisphosphatase (Zimmermann et al. 1976, Eur. J. Biochem. 70, 361–367) the affinity for ligands remained unchanged in the dithiothreitol-activated and in the non-activated state. The activity of PRK was increasingly sensitive to inhibition by 3-phosphoglyceric acid with decreasing pH below pH 8.0.Abbreviations DTT
dithiothreitol
- EDTA
ethylenediamine-tetraacetic acid
- PRK
phosphoribulokinase
- Ru5P
ribulose-5-phosphate
- SDS-PAGE
sodium dodecyl sulfate-polyacryl-amide gel electrophoresis 相似文献
53.
Summary The localization of galactosyl residues and lectin binding sites in mucilage and cell walls of the colony forming green algaCosmocladium saxonicum (Desmidiaceae) has been studied using fluorescent probes. In mucilaginous filaments, which are secreted through pores of the cell wall, and in the primary cell wall galactosyl residues in -bound configuration are exposed, as indicated by indirect immunofluorescence using antiserum to monogalactosyl diglyceride residues. Concanavalin A receptors are present mainly at the surface of the secondary cell wall, whereasRicinus communis agglutinin, type I, receptors are predominantly associated with mucilaginous connecting strands, which join adjacent cells within a colony. NoUlex europaeus agglutinin receptors were found. Application of the fluorochrome calcofluor white ST resulted in labeling both, the primary and the secondary cell wall. The data, obtained with the fluorescent probes were compared with those obtained by thin layer chromatography of hydrolysed mucilage.This work includes parts of a doctoral thesis of B. S. carried out under the supervision of Prof. Dr. M.Mix. 相似文献
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Schwaiger FW; Weyers E; Buitkamp J; Ede AJ; Crawford A; Epplen JT 《Molecular biology and evolution》1994,11(2):239-249
Exon 2 sequences of an expressed MHC-DRB locus from sheep were examined for
polymorphisms in both the antigen-binding regions and the adjacent intronic
mixed simple tandem repeat. Twenty-one novel exon 2 Ovar-DRB alleles were
identified. Short nucleotide motifs are extensively shared between certain
exon 2 regions of Ovar-DRB alleles. The simple repeat variations, the
number of different amino acids at usually polymorphic sites, and the
number of silent substitutions were reduced in the intraspecies analyses of
sheep DRB sequences, compared with those of cattle and goats. It was
paradoxical that the abundance of different sheep alleles was similar to
that of cattle and goats. This paradox may be explained by postulating a
relatively small number of "ancient" alleles, with the present-day Ovar-DRB
alleles being generated by reciprocal exchange of nucleotide motifs. At the
antigen-binding sites, new combinations of amino acids were maintained in
Ovar-DRB alleles by strong positive selection. In sheep--and less
pronounced in goats and cattle--the DRB alleles can be divided into two
groups. In one group, silent substitutions are increased when compared with
the other. This suggests separate evolutionary pathways for certain groups
of DRB alleles within a species. The simple repetitive sequences are also
discussed with respect to the evolution of DRB alleles.
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Valerie Crowell Olivier JT Briët Diggory Hardy Nakul Chitnis Nicolas Maire Aurelio Di Pasquale Thomas A Smith 《Malaria journal》2013,12(1):1-14
Background
Past experience and modelling suggest that, in most cases, mass treatment strategies are not likely to succeed in interrupting Plasmodium falciparum malaria transmission. However, this does not preclude their use to reduce disease burden. Mass screening and treatment (MSAT) is preferred to mass drug administration (MDA), as the latter involves massive over-use of drugs. This paper reports simulations of the incremental cost-effectiveness of well-conducted MSAT campaigns as a strategy for P. falciparum malaria disease-burden reduction in settings with varying receptivity (ability of the combined vector population in a setting to transmit disease) and access to case management.Methods
MSAT incremental cost-effectiveness ratios (ICERs) were estimated in different sub-Saharan African settings using simulation models of the dynamics of malaria and a literature-based MSAT cost estimate. Imported infections were simulated at a rate of two per 1,000 population per annum. These estimates were compared to the ICERs of scaling up case management or insecticide-treated net (ITN) coverage in each baseline health system, in the absence of MSAT.Results
MSAT averted most episodes, and resulted in the lowest ICERs, in settings with a moderate level of disease burden. At a low pre-intervention entomological inoculation rate (EIR) of two infectious bites per adult per annum (IBPAPA) MSAT was never more cost-effective than scaling up ITNs or case management coverage. However, at pre-intervention entomological inoculation rates (EIRs) of 20 and 50 IBPAPA and ITN coverage levels of 40 or 60%, respectively, the ICER of MSAT was similar to that of scaling up ITN coverage further.Conclusions
In all the transmission settings considered, achieving a minimal level of ITN coverage is a “best buy”. At low transmission, MSAT probably is not worth considering. Instead, MSAT may be suitable at medium to high levels of transmission and at moderate ITN coverage. If undertaken as a burden-reducing intervention, MSAT should be continued indefinitely and should complement, not replace, case management and vector control interventions. 相似文献59.
Fernanda C. Dórea C. Anne Muckle David Kelton JT. McClure Beverly J. McEwen W. Bruce McNab Javier Sanchez Crawford W. Revie 《PloS one》2013,8(3)
Background
Recent focus on earlier detection of pathogen introduction in human and animal populations has led to the development of surveillance systems based on automated monitoring of health data. Real- or near real-time monitoring of pre-diagnostic data requires automated classification of records into syndromes–syndromic surveillance–using algorithms that incorporate medical knowledge in a reliable and efficient way, while remaining comprehensible to end users.Methods
This paper describes the application of two of machine learning (Naïve Bayes and Decision Trees) and rule-based methods to extract syndromic information from laboratory test requests submitted to a veterinary diagnostic laboratory.Results
High performance (F1-macro = 0.9995) was achieved through the use of a rule-based syndrome classifier, based on rule induction followed by manual modification during the construction phase, which also resulted in clear interpretability of the resulting classification process. An unmodified rule induction algorithm achieved an F1-micro score of 0.979 though this fell to 0.677 when performance for individual classes was averaged in an unweighted manner (F1-macro), due to the fact that the algorithm failed to learn 3 of the 16 classes from the training set. Decision Trees showed equal interpretability to the rule-based approaches, but achieved an F1-micro score of 0.923 (falling to 0.311 when classes are given equal weight). A Naïve Bayes classifier learned all classes and achieved high performance (F1-micro = 0.994 and F1-macro = .955), however the classification process is not transparent to the domain experts.Conclusion
The use of a manually customised rule set allowed for the development of a system for classification of laboratory tests into syndromic groups with very high performance, and high interpretability by the domain experts. Further research is required to develop internal validation rules in order to establish automated methods to update model rules without user input. 相似文献60.
David JT. Campbell Paul E. Ronksley Braden J. Manns Marcello Tonelli Claudia Sanmartin Robert G. Weaver Deirdre Hennessy Kathryn King-Shier Tavis Campbell Brenda R. Hemmelgarn for the Interdisciplinary Chronic Disease Collaboration 《PloS one》2014,9(4)