The mechanism for activation of GTP hydrolysis on the ribosome     

Voorhees RM  Schmeing TM  Kelley AC  Ramakrishnan V 《Science (New York, N.Y.)》2010,330(6005):835-838

Protein synthesis requires several guanosine triphosphatase (GTPase) factors, including elongation factor Tu (EF-Tu), which delivers aminoacyl-transfer RNAs (tRNAs) to the ribosome. To understand how the ribosome triggers GTP hydrolysis in translational GTPases, we have determined the crystal structure of EF-Tu and aminoacyl-tRNA bound to the ribosome with a GTP analog, to 3.2 angstrom resolution. EF-Tu is in its active conformation, the switch I loop is ordered, and the catalytic histidine is coordinating the nucleophilic water in position for inline attack on the γ-phosphate of GTP. This activated conformation is due to a critical and conserved interaction of the histidine with A2662 of the sarcin-ricin loop of the 23S ribosomal RNA. The structure suggests a universal mechanism for GTPase activation and hydrolysis in translational GTPases on the ribosome.  相似文献   

Integrative analysis of the Caenorhabditis elegans genome by the modENCODE project     

Gerstein MB  Lu ZJ  Van Nostrand EL  Cheng C  Arshinoff BI  Liu T  Yip KY  Robilotto R  Rechtsteiner A  Ikegami K  Alves P  Chateigner A  Perry M  Morris M  Auerbach RK  Feng X  Leng J  Vielle A  Niu W  Rhrissorrakrai K  Agarwal A  Alexander RP  Barber G  Brdlik CM  Brennan J  Brouillet JJ  Carr A  Cheung MS  Clawson H  Contrino S  Dannenberg LO  Dernburg AF  Desai A  Dick L  Dosé AC  Du J  Egelhofer T  Ercan S  Euskirchen G  Ewing B  Feingold EA  Gassmann R  Good PJ  Green P  Gullier F  Gutwein M  Guyer MS  Habegger L  Han T  Henikoff JG 《Science (New York, N.Y.)》2010,330(6012):1775-1787

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Oxygen doping modifies near-infrared band gaps in fluorescent single-walled carbon nanotubes     

Ghosh S  Bachilo SM  Simonette RA  Beckingham KM  Weisman RB 《Science (New York, N.Y.)》2010,330(6011):1656-1659

Controlled chemical modifications of single-walled carbon nanotubes (SWCNTs) that tune their useful properties have been sought for multiple applications. We found that beneficial optical changes in SWCNTs resulted from introducing low concentrations of oxygen atoms. Stable covalently oxygen-doped nanotubes were prepared by exposure to ozone and then light. Treated samples showed distinct, structure-specific near-infrared fluorescence at wavelengths 10 to 15% longer than displayed by pristine semiconducting SWCNTs. Dopant sites harvest light energy absorbed in undoped nanotube regions by trapping mobile excitons. The oxygen-doped SWCNTs are much easier to detect and image than pristine SWCNTs because they give stronger near-infrared emission and do not absorb at the shifted emission wavelength.  相似文献   

Historical fire and vegetation dynamics in dry forests of the interior Pacific Northwest,USA, and relationships to Northern Spotted Owl (Strix occidentalis caurina) habitat conservation     

Rebecca S.H. Kennedy  Michael C. Wimberly 《Forest Ecology and Management》2009

Regional conservation planning frequently relies on general assumptions about historical disturbance regimes to inform decisions about landscape restoration, reserve allocations, and landscape management. Spatially explicit simulations of landscape dynamics provide quantitative estimates of landscape structure and allow for the testing of alternative scenarios. We used a landscape fire succession model to estimate the historical range of variability of vegetation and fire in a dry forest landscape (size ca. 7900 km²) where the present-day risk of high severity fire threatens the persistence of older closed canopy forest which may serve as Northern Spotted Owl (Strix occidentalis caurina) habitat. Our results indicated that historically, older forest may have comprised the largest percentage of the landscape (∼35%), followed by early successional forest (∼25%), with about 9% of the landscape in a closed canopy older forest condition. The amount and condition of older forest varied by potential vegetation type and land use allocation type. Vegetation successional stages had fine-grained spatial heterogeneity in patch characteristics, with older forest tending to have the largest patch sizes among the successional stages. Increasing fire severities posed a greater risk to Northern Spotted Owl habitat than increasing fire sizes or frequencies under historical fire regimes. Improved understanding of historical landscape-specific fire and vegetation conditions and their variability can assist forest managers to promote landscape resilience and increases of older forest, in dry forests with restricted amounts of habitat for sensitive species.  相似文献   

Forest management and temporal effects on food abundance for a ground-foraging bird (Catharus guttatus)     

Jason C. Johnston  Rebecca L. Holberton 《Forest Ecology and Management》2009,258(7):1516-1527

While food abundance is known to limit bird populations, few studies have simultaneously examined both temporal and habitat-related variation in food abundance for ground-foraging birds. We surveyed ground-dwelling arthropods throughout the breeding season and in three forest harvest types (clearcut, selection, and shelterwood stands managed for spruce, fir and hemlock) at the Penobscot Experimental Forest (PEF), Bradley, Maine, USA. Pitfall trapping during 2003 and 2004 was used to measure seasonal and habitat-related variation in abundance of ground-dwelling arthropod food items for hermit thrushes. Arthropods were sorted into relevant taxonomic and size class categories based on the known diet of hermit thrushes. Habitat variables included forest management type, stand-level structure and composition of tree species, and microhabitat measures in a 1 m² area around the pitfall traps. We used redundancy analysis to find stand-level and microhabitat measures that best explained variation in arthropod abundance during 2004. The majority of arthropod captures comprised three groups: ants (Formicidae, 44%), ground beetles (Carabidae, 13%), and spiders (Araneae, 11%). There was significant temporal variation in captures for many taxa. Notably, there were as many as six times more Araneae in early compared to late season samples suggesting the importance of Araneae to ground-foraging birds. Carabidae were more abundant in selection versus either shelterwood or clearcut stands on one sample date. Conversely, Formicidae and Curculionidae were more abundant in shelterwood plots on one and three sampling dates, respectively. Overall, our data provided little evidence that forest management type impacts arthropod food abundance, in stands 5–20 years post-harvest. Abundance of Carabidae was positively correlated with the number of softwoods less than 5 cm DBH and the number of hardwoods greater than 10 cm DBH, while abundance of Formicidae and Homopterans was negatively associated with these same measures. Several taxa were negatively associated with percent of the 1 m² around the pitfall that was shaded, including Araneae, Carabidae, Formicidae, and Staphylinidae. These results suggest that less-shaded forest microhabitats are important areas of increased food abundance for ground-foraging birds, regardless of forest management type or tree composition. Consequently, forest managers seeking to maximize food abundance for ground-foraging birds in managed spruce-fir forests should consider retaining some large diameter hardwood trees and use management techniques that reduce forest floor shading.  相似文献   

Feline nasopharyngeal polyps.     

Rebecca K Muilenburg  Thomas R Fry 《Veterinary Clinics of North America: Small Animal Practice》2002,32(4):839-849

In summary, an ideal diagnostic plan for cats with suspected FNPs should include a thorough anesthetized oropharyngeal examination, otoscopic examination, and imaging studies, which may consist of a bulla radiographic series or specialized imaging studies such as CT or MR scans. In general, if signs indicative of otitis media are present, ventral bulla osteotomy should be advised. As a result of the distinct appearance of FNPs, a preoperative biopsy is not indicated in all instances but should be considered if there are atypical features to the history or presentation. Traction-avulsion of polyps through the external ear canal or auditory tube from the oropharynx may have a lower success rate than traction-avulsion combined with ventral bulla osteotomy. If the veterinarian opts to treat FNPs by traction-avulsion alone as a result of financial constraints imposed by the client, the client should be strongly cautioned regarding potential recurrence. Postoperative complications are possible with any treatment option, but neurologic impairment, including Horner's syndrome, facial neuropathy, and hypoglossal neuropathy, is significantly more likely after surgical intervention by ventral bulla osteotomy than after traction-avulsion alone. A high percentage of these complications are self-limiting. In all instances, appropriate culture and sensitivity and biopsy specimens should be collected so as to enable provision of appropriate postoperative care. Antibiotic therapy should be provided based on culture and sensitivity test results. The use of postoperative steroids to prevent recurrence is controversial.  相似文献   

Esophageal manometry in horses, cows, and sheep during deglutition     

E S Clark  D D Morris  R H Whitlock 《American journal of veterinary research》1987,48(4):547-551

Esophageal pressure events during deglutition were evaluated in healthy adult animals (6 horses, 6 cattle, and 5 sheep), using a 3-side hole catheter assembly perfused with water by use of a hydraulic-capillary infusion system. The peak postdeglutition pressure, contraction time, and contraction length were determined for the cranial and caudal esophageal sphincter regions and for each functionally different region within the body of the esophagus. The percentage of deglutitions in which relaxation developed at the sphincter regions and the propagation speed (velocity at which pressure waves traversed the esophagus) for the regions within the body of the esophagus also were determined. Mean (+/- SEM) resting pressures within the cranial and caudal esophageal sphincter regions in the horse were 84.8 +/- 4.39 and 12.7 +/- 0.61 mm of Hg, respectively, with postdeglutition peaks of 208.0 +/- 4.78 and 100.0 +/- 1.06 mm of Hg, respectively. Peak postdeglutition pressure was 92.3 +/- 1.59 mm of Hg in the cranial two thirds of the esophageal body and 100.9 +/- 1.31 mm of Hg in the caudal third. Mean resting pressure of the cranial esophageal sphincter region in the cow was 82.0 +/- 7.81 mm of Hg, whereas that of the caudal esophageal sphincter region was 20.5 +/- 0.36 mm of Hg. The peak postdeglutition pressures for the cranial esophageal sphincter region, proximal portion of the esophageal body, caudal portion of the esophageal body, and caudal esophageal sphincter region in the bovine esophagus were 238.1 +/- 2.93, 105.4 +/- 1.97, 114.5 +/- 1.49, and 112.0 +/- 1.20 mm of Hg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

Evolution of a microbial acetyltransferase for modification of glyphosate: a novel tolerance strategy   总被引：6，自引：0，他引：6  

Siehl DL  Castle LA  Gorton R  Chen YH  Bertain S  Cho HJ  Keenan R  Liu D  Lassner MW 《Pest management science》2005,61(3):235-240

N-Acetylation is a modification of glyphosate that could potentially be used in transgenic crops, given a suitable acetyltransferase. Weak enzymatic activity (k(cat) = 5 min(-1), K(M) = 1 mM) for N-acetylation of glyphosate was discovered in several strains of Bacillus licheniformis (Weigmann) Chester by screening a microbial collection with a mass spectrometric assay. The parental enzyme conferred no tolerance to glyphosate in any host when expressed as a transgene. Eleven iterations of DNA shuffling resulted in a 7000-fold improvement in catalytic efficiency (k(cat)/K(M)), sufficient for conferring robust tolerance to field rates of glyphosate in transgenic tobacco and maize. In terms of k(cat)/K(M), the native enzyme exhibited weak activity (4-450% of that with glyphosate) with seven of the common amino acids. Evolution of the enzyme towards an improved k(cat)/K(M) for glyphosate resulted in increased activity toward aspartate (40-fold improved k(cat)), but activity with serine and phosphoserine almost completely vanished. No activity was observed among a broad sampling of nucleotides and antibiotics. Improved catalysis with glyphosate coincided with increased thermal stability.  相似文献   

Isolation, characterization, and expression of stromelysin-1 in primary tumors of dogs     

Sorensen KC  Newman RG  Kitchell BE  Schaeffer DJ  Siegel AM 《American journal of veterinary research》2005,66(9):1526-1535

OBJECTIVE: To isolate and characterize the cDNA sequence of canine stromelysin-1 (matrix metalloproteinase [MMPI-3), screen various naturally developing primary tumors of dogs, and assess the effect of stromelysin-1 on survival of dogs with cancer. SAMPLE POPULATION: 3 canine cell lines and biopsy specimens of primary tumors collected from 54 dogs. PROCEDURE: 3 canine cell lines and biopsy specimens of primary tumors collected from 54 dogs at the University of Illinois Veterinary Teaching Hospital were used in the study. Primer sets based on human stromelysin-1 and consensus sequences were designed for expression, screening, and isolation. Two additional primer sets were designed for screening. Samples were assayed at least in duplicate. Data were analyzed for differences in expression of stromelysin-1 on the basis of sex, age, metastasis, malignant versus nonmalignant tissue origin, and duration of patient survival. RESULTS: A 1,479-bp cDNA nucleotide sequence was amplified from established canine cell lines. The open reading frame encoded a protein consisting of 478 amino acids. This sequence was 70% to 88% homologous with stromelysin-1 of other species at the amino acid level. Fifty-four samples were screened for stromelysin-1. Of these, 34 (63%) had positive results and 20 (37%) had negative results for expression. Stromelysin-1 and metastasis were associated with a poor prognosis for survival. CONCLUSIONS AND CLINICAL RELEVANCE: Stromelysin-1 is a potential activator of other members of the MMP family. Additional studies are needed to investigate the relationship between stromelysin-1 production and aggressive biological behavior of tumors in dogs.  相似文献   

Subdural hematoma of the brainstem in a dog: magnetic resonance findings and treatment     

Adamo PF  Crawford JT  Stepien RL 《Journal of the American Animal Hospital Association》2005,41(6):400-405

An 8-year-old, spayed female Dalmatian with a history of seizures was evaluated for cervical pain and bilateral scleral hemorrhages. Diagnostic evaluations revealed a mass displacing the ventral brainstem on magnetic resonance imaging (MRI). The mass was surgically removed and histologically confirmed to be a hematoma. The dog's neurological signs resolved completely after surgery. Although extradural, subdural, subarachnoid, and intraparenchymal hemorrhages have been reported in dogs and cats, this is the first known report of a subdural hematoma of the ventral brainstem in a dog. On the basis of the history and the appearance of the subdural hematoma on MRI, a traumatic event during the seizure episodes was considered the most likely cause of the subdural hematoma in this case.  相似文献