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排序方式: 共有177条查询结果,搜索用时 687 毫秒
1.
Dibutyryl cAMP, aminophylline, and beta-adrenergic agonists protect against pulmonary edema caused by phosgene 总被引:3,自引:0,他引:3
2.
Linker insertion analysis of the FimH adhesin of type 1 fimbriae in an Escherichia coli fimH-null background 总被引:2,自引:0,他引:2
Mark A. Schembri Lars Pallesen Hugh Connell David L. Hasty Per Klemm 《FEMS microbiology letters》1996,137(2-3):257-263
Abstract The gene encoding the Escherichia coli FimH adhesin of type 1 fimbriae has been subjected to linker insertion mutagenesis. Amino acid changes were introduced at a number of positions spanning the entire sequence in order to probe the structure-function relationship of the FimH protein. The effect of these mutations on the ability of bacteria to express a D-mannose binding phenotype was assessed in a fimH null mutant (MS4) constructed by allelic exchange in the E. coli K-12 strain PC31. Mutations mapping at amino acid residues 36, 58 and 279 of the mature FimH protein were shown to completely abolish binding to D-mannose receptors. Differences in the level of fimbriation were also observed as a result of some of the mutations in the fimH gene. These mutants may prove useful in dissecting receptor-ligand interactions by defining regions of the FimH protein that are important in erythrocyte binding. 相似文献
3.
Efficiency of insertion versus replacement vector targeting varies at different chromosomal loci. 总被引:5,自引:2,他引:3
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We have analyzed the targeting frequencies and recombination products generated with isogenic vectors at the fah and fgr loci in embryonic stem cells. A single vector which could be linearized at different sites to generate either a replacement or an insertion vector was constructed for each locus. A replacement event predominated when the vectors were linearized at the edge of the homologous sequences, while an insertion event predominated when the vectors were linearized within the homologous sequences. However, the ratio of the targeting frequencies exhibited by the different vector configurations differed for the two loci. When the fgr vector was linearized as an insertion vector, the ratio of targeted to random integrations was four- to eightfold greater than when the vector was linearized as a replacement vector. By contrast, the ratio of targeted to random integrations at the fah locus did not vary with the linearization site of the vector. The different relationships between the targeting frequency and the vector configuration at the fgr and fah loci may indicate a DNA sequence or chromatin structure preference for different targeting pathways. 相似文献
4.
5.
6.
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.
相似文献
7.
Glycerol-induced unraveling of the tight helical conformation of Escherichia coli type 1 fimbriae.
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S N Abraham M Land S Ponniah R Endres D L Hasty J P Babu 《Journal of bacteriology》1992,174(15):5145-5148
Glycerol was found to unravel the helical conformation of Escherichia coli type 1 fimbriae without appreciable depolymerization. The linearized fimbrial polymers have a diameter of 2 nm, react strongly with a monoclonal antibody directed at an inaccessible epitope on native fimbriae, and display greater mannose-binding activity and trypsin sensitivity than native fimbriae. Removal of glycerol by dialysis results in spontaneous reassembly of the linear polymers into structures morphologically, antigenically, and functionally indistinguishable from native fimbriae. 相似文献
8.
Cartilage regeneration in the adult rabbit ear was examined with respect to glycosaminoglycan (GAG) synthesis at various stages of the regeneration process. Increased hyaluronic acid and chondroitin sulfate synthesis was first seen 31 days after wounding, when a metachromatic cartilage matrix could be distinguished from blastemal cells. Analysis of cartilage and the overlying skin separately showed that 90% of the labeled chondroitin sulfate was found in the cartilage being regenerated. DEAE-cellulose chromatography of GAG preparations from 35-day regenerating cartilages showed hyaluronic acid and chondroitin sulfate peaks eluting in the same position as those isolated from normal cartilages. The identity of the hyaluronic acid and chondroitin sulfate peaks was confirmed by their susceptibility to Streptomyces hyaluronidase and chondroitinase ABC, respectively. Although the degree of sulfation in normal and regenerated cartilages was similar, the ratio of chondroitin 6-sulfate to chondroitin 4-sulfate was increased in regenerated cartilages. GAG preparations from unlabeled cartilages were digested with chondroitinase ABC and the disaccharide digestive products were identified and quantitiated. Normal cartilage had a ratio of 0.27; the same ratio for the regenerated cartilage was 1.58. 相似文献
9.
10.
Sherry G. Dodds Manish Parihar Martin Javors Jia Nie Nicolas Musi Zelton Dave Sharp Paul Hasty 《Aging cell》2020,19(2)
Acarbose blocks the digestion of complex carbohydrates, and the NIA Intervention Testing Program (ITP) found that it improved survival when fed to mice. Yet, we do not know if lifespan extension was caused by its effect on metabolism with regard to the soma or cancer suppression. Cancer caused death for ~80% of ITP mice. The ITP found rapamycin, an inhibitor to the pro‐growth mTORC1 (mechanistic target of rapamycin complex 1) pathway, improved survival and it suppressed tumors in Apc+/Min mice providing a plausible rationale to ask if acarbose had a similar effect. Apc+/Min is a mouse model prone to intestinal polyposis and a mimic of familial adenomatous polyposis in people. Polyp‐associated anemia contributed to their death. To address this knowledge gap, we fed two doses of acarbose to Apc+/Min mice. Acarbose improved median survival at both doses. A cross‐sectional analysis was performed next. At both doses, ACA fed mice exhibited reduced intestinal crypt depth, weight loss despite increased food consumption and reduced postprandial blood glucose and plasma insulin, indicative of improved insulin sensitivity. Dose‐independent and dose‐dependent compensatory liver responses were observed for AMPK and mTORC1 activities, respectively. Only mice fed the high dose diet exhibited reductions in tumor number with higher hematocrits. Because low‐dose acarbose improved lifespan but failed to reduced tumors, its effects seem to be independent of cancer. These data implicate the importance of improved carbohydrate metabolism on survival. 相似文献