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排序方式: 共有117条查询结果,搜索用时 15 毫秒
1.
Genetic variation at the Major Histocompatibility Complex locus DQ beta was
analyzed in 233 beluga whales (Delphinapterus leucas) from seven
populations: St. Lawrence Estuary, eastern Beaufort Sea, eastern Chukchi
Sea, western Hudson Bay, eastern Hudson Bay, southeastern Baffin Island,
and High Arctic and in 12 narwhals (Monodon monoceros) sympatric with the
High Arctic beluga population. Variation was assessed by amplification of
the exon coding for the peptide binding region via the polymerase chain
reaction, followed by either cloning and DNA sequencing or single-stranded
conformation polymorphism analysis. Five alleles were found across the
beluga populations and one in the narwhal. Pairwise comparisons of these
alleles showed a 5:1 ratio of nonsynonymous to synonymous substitutions per
site leading to eight amino acid differences, five of which were
nonconservative substitutions, centered around positions previously shown
to be important for peptide binding. Although the amount of allelic
variation is low when compared with terrestrial mammals, the nature of the
substitutions in the peptide binding sites indicates an important role for
the DQ beta locus in the cellular immune response of beluga whales.
Comparisons of allele frequencies among populations show the High Arctic
population to be different (P < or = .005) from the other beluga
populations surveyed. In these other populations an allele, Dele-DQ
beta*0101-2, was found in 98% of the animals, while in the High Arctic it
was found in only 52% of the animals. Two other alleles were found at high
frequencies in the High Arctic population, one being very similar to the
single allele found in narwhal.
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Antimicrobial resistance is a serious threat to public health that dramatically undermines our ability to treat bacterial infections. Microorganisms exhibit resistance to different drug classes by acquiring resistance determinants through multiple mechanisms including horizontal gene transfer. The presence of drug resistance genotypes is mostly associated with corresponding phenotypic resistance against the particular antibiotic. However, bacterial communities harbouring silent antimicrobial resistance genes—genes whose presence is not associated with a corresponding resistant phenotype do exist. Under suitable conditions, the expression pattern of such genes often revert and regain resistance and could potentially lead to therapeutic failure. We often miss the presence of silent genes, since the current experimental paradigms are focused on resistant strains. Therefore, the knowledge on the prevalence, importance and mechanism of silent antibiotic resistance genes in bacterial pathogens are very limited. Silent genes, therefore, provide an additional level of complexity in the war against drug-resistant bacteria, reminding us that not only phenotypically resistant strains but also susceptible strains should be carefully investigated. In this review, we discuss the presence of silent antimicrobial resistance genes in bacteria, their relevance and their importance in public health. 相似文献
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5.
Raja SM Wang B Dantuluri M Desai UR Demeler B Spiegel K Metkar SS Froelich CJ 《The Journal of biological chemistry》2002,277(51):49523-49530
We have recently shown that the physiological mediator of granule-mediated apoptosis is a macromolecular complex of granzymes and perforin complexed with the chondroitin-sulfate proteoglycan, serglycin (Metkar, S. S., Wang, B., Aguilar-Santelises, M., Raja, S. M., Uhlin-Hansen, L., Podack, E., Trapani, J. A., and Froelich, C. J. (2002) Immunity 16, 417-428). We now report our biophysical studies establishing the nature of granzyme B-serglycin (GrB.SG) complex. Dynamic laser light scattering studies establish that SG has a hydrodynamic radius of approximately 140 +/- 23 nm, comparable to some viral particles. Agarose mobility shift gels and surface plasmon resonance (SPR), show that SG binds tightly to GrB and has the capacity to hold 30-60 GrB molecules. SPR studies also indicate equivalent binding affinities (K(d) approximately 0.8 microm), under acidic (granule pH) and neutral isotonic conditions (extra-cytoplasmic pH), for GrB.SG interaction. Finally, characterization of GrB.SG interactions within granules revealed complexes of two distinct molecular sizes, one held approximately 4-8 molecules of GrB, whereas the other contained as many as 32 molecules of GrB or other granule proteins. These studies provide a firm biophysical basis for our earlier reported observations that the proapoptotic granzyme is exocytosed predominantly as a macromolecular complex with SG. 相似文献
6.
Escherichia coli has two catalases, HPI and HPII. HPI is induced during logarithmic growth in response to low concentrations of hydrogen peroxide. This induction is OxyR-dependent. On the other hand, HPII is not peroxide-inducible but is induced in entry to the stationary phase. We demonstrate here that E. coli displayed higher HPI catalase activity when compared to the cultures that were grown in a normal medium, if grown in a medium supplemented with iron-citrate. Iron supplementation had no effect on HPII catalase. This increase of HPI activity was OxyR-independent and not observed in a Deltafur mutant. The physiological significance of the increase of HPI activity is unclear, but it appears that the katG gene that codes for HPI catalase is among the genes that are regulated by Fur. 相似文献
7.
Influence of the MexAB-OprM Multidrug Efflux System on Quorum Sensing in Pseudomonas aeruginosa 总被引:6,自引:0,他引:6
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Kelly Evans Luciano Passador Ramakrishnan Srikumar Eric Tsang Jonathon Nezezon Keith Poole 《Journal of bacteriology》1998,180(20):5443-5447
Pseudomonas aeruginosa nalB mutants which hyperexpress the MexAB-OprM multidrug efflux system produce reduced levels of several extracellular virulence factors known to be regulated by quorum sensing. Such mutants also produce less acylated homoserine lactone autoinducer PAI-1, consistent with an observed reduction in lasI expression. These data suggest that PAI-1 is a substrate for MexAB-OprM, and its resulting exclusion from cells hyperexpressing MexAB-OprM limits PAI-1-dependent activation of lasI and the virulence genes. 相似文献
8.
Elongation factor-1 alpha occurs as two copies in bees: implications for phylogenetic analysis of EF-1 alpha sequences in insects 总被引:5,自引:1,他引:4
We report the complete sequence of a paralogous copy of elongation factor-1
alpha (EF-1 alpha) in the honeybee, Apis mellifera (Hymenoptera: Apidae).
This copy differs from a previously described copy in the positions of five
introns and in 25% of the nucleotide sites in the coding regions. The
existence of two paralogous copies of EF-1 alpha in Drosophila and Apis
suggests that two copies of EF-1 alpha may be widespread in the
holometabolous insect orders. To distinguish between a single, ancient gene
duplication and parallel, independent fly and bee gene duplications, we
performed a phylogenetic analysis of hexapod EF-1 alpha sequences.
Unweighted parsimony analysis of nucleotide sequences suggests an ancient
gene duplication event, whereas weighted parsimony analysis of nucleotides
and unweighted parsimony analysis of amino acids suggests the contrary:
that EF-1 alpha underwent parallel gene duplications in the Diptera and the
Hymenoptera. The hypothesis of parallel gene duplication is supported both
by congruence among nucleotide and amino acid data sets and by
topology-dependent permutation tail probability (T-PTP) tests. The
resulting tree topologies are also congruent with current views on the
relationships among the holometabolous orders included in this study
(Diptera, Hymenoptera, and Lepidoptera). More sequences, from diverse
orders of holometabolous insects, will be needed to more accurately assess
the historical patterns of gene duplication in EF-1 alpha.
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9.
The use of ubiquitin lysine mutants to characterize E2–E3 linkage specificity: Mass spectrometry offers a cautionary “tail”
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Oligomeric ubiquitin structures (i.e. ubiquitin “chains”) may be formed through any of seven different lysine residues in the polypeptide, or via the amine group of Met 1. Different types of ubiquitin chains can confer very different biological outcomes to a protein substrate, yet the structural characteristics of E2s and E3s that determine ubiquitin linkage specificity remain poorly understood. In vitro autoubiquitylation assays combined with ubiquitin protein variants bearing individually mutated lysine residues (“K‐to‐R” mutants) have thus been widely used to characterize E2–E3 linkage specificity. However, how this type of assay compares to direct identification of ubiquitin linkage types using mass spectrometry (MS) has not been rigorously tested. Here, we characterize the linkage specificity of 12 different E2–E3 combinations using both approaches. The simple MS‐based method described here is more robust, requires less material and is less prone to bias introduced by, e.g. the use of mutant proteins with unknown effects on E1, E2 or E3 recognition, antibodies with uncharacterized epitopes, the low dynamic range of X‐ray film, and additional sources of experimental error. Indeed, our results suggest that the K‐to‐R assay be approached with some caution. 相似文献
10.