Structures of the bacterial ribosome in classical and hybrid states of tRNA binding     

Dunkle JA  Wang L  Feldman MB  Pulk A  Chen VB  Kapral GJ  Noeske J  Richardson JS  Blanchard SC  Cate JH 《Science (New York, N.Y.)》2011,332(6032):981-984

During protein synthesis, the ribosome controls the movement of tRNA and mRNA by means of large-scale structural rearrangements. We describe structures of the intact bacterial ribosome from Escherichia coli that reveal how the ribosome binds tRNA in two functionally distinct states, determined to a resolution of ~3.2 angstroms by means of x-ray crystallography. One state positions tRNA in the peptidyl-tRNA binding site. The second, a fully rotated state, is stabilized by ribosome recycling factor and binds tRNA in a highly bent conformation in a hybrid peptidyl/exit site. The structures help to explain how the ratchet-like motion of the two ribosomal subunits contributes to the mechanisms of translocation, termination, and ribosome recycling.  相似文献   

Spin disorder on a triangular lattice     

Nakatsuji S  Nambu Y  Tonomura H  Sakai O  Jonas S  Broholm C  Tsunetsugu H  Qiu Y  Maeno Y 《Science (New York, N.Y.)》2005,309(5741):1697-1700

As liquids crystallize into solids on cooling, spins in magnets generally form periodic order. However, three decades ago, it was theoretically proposed that spins on a triangular lattice form a liquidlike disordered state at low temperatures. Whether or not a spin liquid is stabilized by geometrical frustration has remained an active point of inquiry ever since. Our thermodynamic and neutron measurements on NiGa2S4, a rare example of a two-dimensional triangular lattice antiferromagnet, demonstrate that geometrical frustration stabilizes a low-temperature spin-disordered state with coherence beyond the two-spin correlation length. Spin liquid formation may be an origin of such behavior.  相似文献   

Human neuroblasts migrate to the olfactory bulb via a lateral ventricular extension   总被引：3，自引：0，他引：3  

Curtis MA  Kam M  Nannmark U  Anderson MF  Axell MZ  Wikkelso C  Holtås S  van Roon-Mom WM  Björk-Eriksson T  Nordborg C  Frisén J  Dragunow M  Faull RL  Eriksson PS 《Science (New York, N.Y.)》2007,315(5816):1243-1249

The rostral migratory stream (RMS) is the main pathway by which newly born subventricular zone cells reach the olfactory bulb (OB) in rodents. However, the RMS in the adult human brain has been elusive. We demonstrate the presence of a human RMS, which is unexpectedly organized around a lateral ventricular extension reaching the OB, and illustrate the neuroblasts in it. The RMS ensheathing the lateral olfactory ventricular extension, as seen by magnetic resonance imaging, cell-specific markers, and electron microscopy, contains progenitor cells with migratory characteristics and cells that incorporate 5-bromo-2'-deoxyuridine and become mature neurons in the OB.  相似文献   

Efficient inhibition of the Alzheimer's disease beta-secretase by membrane targeting     

Rajendran L  Schneider A  Schlechtingen G  Weidlich S  Ries J  Braxmeier T  Schwille P  Schulz JB  Schroeder C  Simons M  Jennings G  Knölker HJ  Simons K 《Science (New York, N.Y.)》2008,320(5875):520-523

beta-Secretase plays a critical role in beta-amyloid formation and thus provides a therapeutic target for Alzheimer's disease. Inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of active enzyme. We have addressed this issue by synthesizing a membrane-anchored version of a beta-secretase transition-state inhibitor by linking it to a sterol moiety. Thus, we targeted the inhibitor to active beta-secretase found in endosomes and also reduced the dimensionality of the inhibitor, increasing its local membrane concentration. This inhibitor reduced enzyme activity much more efficiently than did the free inhibitor in cultured cells and in vivo. In addition to effectively targeting beta-secretase, this strategy could also be used in designing potent drugs against other membrane protein targets.  相似文献   

Application of Relaxed Eddy Accumulation Technique to Quantify Hg0 Fluxes Over Modified Soil Surfaces     

Marcus Olofsson  Jonas Sommar  Evert Ljungström  Maria Andersson  Ingvar Wängberg 《Water, air, and soil pollution》2005,167(1-4):331-352

Fluxes of mercury from a waste repository and from an agricultural field amended with sewage sludge were measured. The measurements were performed by utilising a Relaxed Eddy Accumulation (REA) system synchronously coupled to automated mercury cold vapour atomic fluorescence analysers (CVAFA). The waste repository was severely contaminated and fluxes of between 0.16μg m^?2 h^?1 and 29μg m^?2 h^?1 could be measured. Fluxes at the slightly contaminated agricultural field measured between 8 ng m^?2 h^?1 and 1.9μg m^?2 h^?1. The results showed that the REA-CVAFA system could be used for measurements above both severely-and slightly contaminated soils. The measurements at the chlor-alkali plant showed that temperature was the most important parameter controlling the release of mercury at this site. At the agricultural field, the measurements indicated that both solar radiation and temperature may have influenced the emissions. Most of the mercury added to the field was lost to the atmosphere during the summer season.  相似文献   

Improving the detection of rare native fish species in environmental DNA metabarcoding surveys     

Jack Rojahn  Dianne M. Gleeson  Elise Furlan  Tim Haeusler  Jonas Bylemans 《水产资源保护:海洋与淡水生态系统》2021,31(4):990-997

1. The presence of threatened or endangered species often strongly influences management and conservation decisions. Within the Murray–Darling Basin (MDB), Australia, the presence of threatened native fish affects the management and allocation of water resources. In New South Wales, these decisions are currently based on traditional fisheries data and a predictive MaxEnt model. However, it is important to verify the model's predictive power given the implication it may have, but this requires methods with a high detection sensitivity for rare species.
2. Although the use of environmental DNA (eDNA) monitoring, in particular eDNA metabarcoding, achieves a higher detection sensitivity compared with traditional methods, earlier surveys in the MDB have shown that the highly abundant and invasive common carp (Cyprinus carpio) can reduce detection probabilities for rare species. Consequently, a polymerase chain reaction (PCR) blocking primer designed to block the amplification of carp eDNA could increase the detection probabilities for rare native species while simultaneously reducing the required sampling effort and survey costs. Although PCR blocking primers are often used in ancient DNA and dietary studies, no aquatic eDNA metabarcoding study to date has evaluated the potential benefits of using PCR blocking primers.
3. A laboratory and field-based pilot study was used to address this knowledge gap and assess the impact of a blocking primer, targeting cyprinid fishes (including carp), on the detection probabilities of native species and the minimum sampling effort required.
4. Results showed that the inclusion of the blocking primer increased the detection probabilities for native species by 10–20% and reduced the minimum required sampling effort by 25–50%. These findings provide important insights into possible methods for optimizing eDNA metabarcoding surveys for the detection of rare aquatic species.

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Latitudinal differences in the duration of development of Neocalanus plumchrus copepodites     

Sonia D. Batten  David W. Welch  Tanya Jonas 《Fisheries Oceanography》2003,12(3):201-208

Quasi‐synoptic sampling along a transect from Alaska to California carried out in spring and summer 2000 using Continuous Plankton Recorders reveals that the abundant calanoid copepod Neocalanus plumchrus (Marukawa) reaches the surface at approximately the same time across the region. However, monthly sampling also reveals that the timing of peak biomass (when 50% of the population consists of copepodites at stage CV) occurs about 5 weeks earlier at the southernmost part of its range than at the northernmost part, with intermediate areas having intermediate timings. Surface water temperature differed by about 4°C between the warmer south and the cooler north, and we suggest that such a difference would reduce development duration by about 3 weeks. If food supply in the north is more conducive to lipid accumulation, as seems possible from phytoplankton biomass data, then the use of the differences in timing of peak N. plumchrus biomass in each area as a measure of the differences in development time may not be accurate. We find that the estimate of the time of peak biomass varying by about 5 weeks between north and south may be an exaggeration of the actual difference in the development duration. Temperature is probably the most important factor governing the shorter development duration of N. plumchrus in southern latitudes.  相似文献   

Factors affecting the probability of windthrow at stand level as a result of Gudrun winter storm in southern Sweden     

Erik Valinger  Jonas Fridman 《Forest Ecology and Management》2011,262(3):398-403

A storm in January 2005 in southern Sweden (Gudrun) caused large damage to forests, archaeological sites, buildings, power supply, telecommunications, and infrastructure. In this work, we analyzed the factors affecting the probability of windthrow at stand level (i.e. tree- and stand characteristics) in southern Sweden. We selected a sub-sample (1721 plots) of existing plots from the Swedish National Forest Inventory (inventoried in 2003 and 2004). To assess whether these plots had suffered damage or not, aerial photographs were taken in summer 2005. In order to analyze the effects of measured characteristics on damage, field data for each sub-sample plot were merged with the corresponding result of the aerial photo interpretation.We found that the plots damaged were typically well stocked mature stands, dominated by Norway spruce (Picea abies (L.) Karst.), and often also recently thinned. Probability of damage increased with increase in stand height. In mixed stands, decrease of proportion of Norway spruce decreased the probability of damage. An admixture of deciduous trees, leafless in this winter storm, showed larger effect in this sense than that of Scots pine.  相似文献   

Antibiotic resistance patterns in fecal bacteria isolated from Christmas shearwater (Puffinus nativitatis) and masked booby (Sula dactylatra) at remote Easter Island     

Ardiles-Villegas K  González-Acuña D  Waldenström J  Olsen B  Hernández J 《Avian diseases》2011,55(3):486-489

Antibiotic use and its implications have been discussed extensively in the past decades. This situation has global consequences when antibiotic resistance becomes widespread in the intestinal bacterial flora of stationary and migratory birds. This study investigated the incidence of fecal bacteria and general antibiotic resistance, with special focus on extended spectrum beta-lactamase (ESBL) isolates, in two species of seabirds at remote Easter Island. We identified 11 species of bacteria from masked booby (Sula dactylatra) and Christmas shearwater (Puffinus nativitatis); five species of gram-negative bacilli, four species of Streptococcus (Enterococcus), and 2 species of Staphylococcus. In addition, 6 types of bacteria were determined barely to the genus level. General antibiotic susceptibility was measured in the 30 isolated Enterobacteriaceae to 11 antibiotics used in human and veterinary medicine. The 10 isolates that showed a phenotypic ESBL profile were verified by clavulanic acid inhibition in double mixture discs with cefpodoxime, and two ESBL strains were found, one strain in masked booby and one strain in Christmas shearwater. The two bacteria harboring the ESBL type were identified as Serratia odorifera biotype 1, which has zoonotic importance. Despite minimal human presence in the masked booby and Christmas shearwater habitats, and the extreme geographic isolation of Easter Island, we found several multiresistant bacteria and even two isolates with ESBL phenotypes. The finding of ESBLs has animal and public health significance and is of potential concern, especially because the investigation was limited in size and indicated that antibiotic-resistant bacteria now are distributed globally.  相似文献   

High prevalence of antibiotic resistance in pathogenic Escherichia coli from large- and small-scale poultry farms in Bangladesh     

Hasan B  Faruque R  Drobni M  Waldenström J  Sadique A  Ahmed KU  Islam Z  Parvez MB  Olsen B  Alam M 《Avian diseases》2011,55(4):689-692

Antibiotic resistance in avian bacterial pathogens is a common problem in the Bangladesh poultry industry. The aim of the present study was to provide information on the present status of antibiotic resistance patterns in avian pathogenic Escherichia coli in Bangladesh. Of 279 dead or sick poultry of different ages, 101 pathogenic E coli strains isolated from broilers and layer hens with colibacillosis infections were screened to determine phenotypic expression of antimicrobial resistance against 13 antibiotics used in both veterinary and human medicine in Bangladesh. Of 101 pathogenic E. coli isolates, more than 55% were resistant to at least one or more of the tested compounds, and 36.6% of the isolates showed multiple-drug-resistant phenotypes. The most common resistances observed were against tetracycline (45.5%), trimethoprim-sulphamethoxazole (26.7%), nalidixic acid (25.7%), ampicillin (25.7%), and streptomycin (20.8%). Resistance to ciprofloxacin (12.9%), chlormaphenicol (8.9%), nitrofurantoin (2%), and gentamicin (2%) was also observed, and none of the isolates were resistant to tigecycline as well as extended spectrum beta-lactamase (ESBL) producers. One isolate was resistant to cefuroxime (1%), cefadroxil (1%), and mecillinam (1%) but was not an ESBL producer. Resistance rates, although significant in Bangladeshi isolates, were found to be lower than those reported for avian isolates from the Republic of Korea and clinical, avian, and environmental isolates from Bangladesh. The high level of antibiotic resistance in avian pathogens from Bangladesh is worrisome and indicates that widespread use of antibiotics as feed additives for growth promotion and disease prevention could have negative implications for human and animal health and the environment.  相似文献