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排序方式: 共有189条查询结果,搜索用时 31 毫秒
1.
The function of selenocysteine synthase and SELB in the synthesis and incorporation of selenocysteine. 总被引:4,自引:0,他引:4
The selAB operon codes for the proteins selenocysteine synthase and SELB which catalyse the synthesis and cotranslational insertion of selenocysteine into protein. This communication deals with the biochemical characterisation of these proteins and in particular with their specific interaction with the selenocysteine-incorporating tRNA(Sec). Selenocysteine synthase catalyses the synthesis of selenocysteyl-tRNA(Sec) from seryl-tRNA(Sec) in a pyridoxal phosphate-dependent reaction mechanism. The enzyme specifically recognizes the tRNA(Sec) molecule; a cooperative interaction between the tRNA binding site and the catalytically active pyridoxal phosphate site is suggested. SELB is an EF-Tu-like protein which specifically complexes selenocysteyl-tRNA(Sec). Interaction with the selenol group of the side chain of the aminoacylated residue is a prerequisite for the formation of a stable SELB.tRNA complex. Mechanistically, this provides the biochemical basis for the exclusive selection of selenocysteyl-tRNA(Sec) in the decoding step of a selenocysteine-specific UGA triplet. 相似文献
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Patterns of Root Colonization in Epacridaceous Plants Collected from Different Sites 总被引:2,自引:0,他引:2
Root colonization was studied in ten species of the Epacridaceaeat three sites in Victoria by morphological and cross-inoculationexperiments. The sites and genera chosen were Cranbourne [Epacrisimpressa Labill. andLeucopogon ericoides(Smith) R. Br.] andRye [L. parviflorus(Andrews) Lindley] on the Mornington Peninsula,and the Grampians[Astroloma conostephioides(Sond.) Benth.,A.humifusum(Cav.) R. Br.,A pinifolium(R. Br.) Benth,Brachylomadaphnoides(Smith) Benth.,E. impressa, E. impressavar.grandifloraBenth.andStyphelia adscendensR. Br.] in western Victoria. For morphologicalstudies, samples of roots from each species at each site werecleared and stained and examined microscopically. For cross-inoculationstudies, cuttings from each site were struck in potting mediuminoculated with soil from the same and other sites. The ericoidmycorrhizae in the roots of plants found at or grown in Cranbourneand Rye soils were similar. Both were significantly differentfrom the internal hyphae found in the roots of plants foundat or grown in Grampians soils, which were three times largerin diameter and formed dense coils which filled the host celland invaded adjacent epidermal cells. This suggests that morethan one fungus is involved in the relationships, that the MorningtonPeninsula sites had a different fungus from the Grampians siteand that host specificity is low. Vesicular structures werealso found commonly on plants at the Grampians site, in contrastwith other sites. Epacridaceae; root; fungus; mycorrhiza; morphology; inoculation 相似文献
4.
This communication identifies, for the first time, a receptor protein for signal perception from the P(II) signal transduction protein in the cyanobacterium Synechococcus elongatus. P(II), a phosphoprotein that signals the carbon/nitrogen status of the cells, forms a tight complex with the key enzyme of the arginine biosynthetic pathway, N-acetylglutamate (NAG) kinase. In complex with P(II), the catalytic activity of NAG kinase is strongly enhanced. Complex formation does not require the effector molecules of P(II), 2-oxoglutarate and ATP, but it is highly susceptible to modifications at the phosphorylation site of P(II), Ser-49. Stable complexes were only formed with the non-phosphorylated form of P(II) but not with Ser-49 mutants. In accordance with these data, NAG kinase activity in S. elongatus extracts correlated with the phosphorylation state of P(II), with high NAG kinase activities corresponding to non-phosphorylated P(II) (nitrogen-excess conditions) and low activities to increased levels of P(II) phosphorylation (nitrogen-poor conditions), thus subjecting the key enzyme of arginine biosynthesis to global nitrogen control. 相似文献
5.
This communication presents a short outline of the current knowledge on the molecular basis of PII signal transduction in unicellular cyanobacteria with respect to the perception of environmental stimuli. First, the general characteristics of the PII signalling system in unicellular cyanobacteria are presented, the hallmark of which is modification by serine-phosphorylation, as compared to the paradigmatic PII signal transduction system in proteobacteria, which is based on tyrosyl-uridylylation. Then, the focus is turned on the signals controlling PII phosphorylation state. Recently, the cellular phosphatase (termed PphA), which specifically dephosphorylates phosphorylated PII (PII -P) was identified in Synechocystis sp. strain PCC 6803. With the availability of a PphA-deficient mutant and the purified components for in vitro assay of PphA mediated PII -P dephosphorylation, novel insights into the signals, to which PII -P dephosphorylation responds, can be obtained. Here we present an investigation of the response of PII -P dephosphorylation towards treatments that affect the redox-balance of the cells. Furthermore, a possible role of varying ATP/ADP ratios on PII -P dephosphorylation was examined. From these studies, together with previous investigations, we conclude that PII -P dephosphorylation specifically responds to changes in the levels of central metabolites of carbon metabolism, in particular 2-oxoglutarate. 相似文献
6.
The timing of life-history events in a changing climate 总被引:7,自引:0,他引:7
Post E Forchhammer MC Stenseth NC Callaghan TV 《Proceedings. Biological sciences / The Royal Society》2001,268(1462):15-23
Although empirical and theoretical studies suggest that climate influences the timing of life-history events in animals and plants, correlations between climate and the timing of events such as egg-laying, migration or flowering do not reveal the mechanisms by which natural selection operates on life-history events. We present a general autoregressive model of the timing of life-history events in relation to variation in global climate that, like autoregressive models of population dynamics, allows for a more mechanistic understanding of the roles of climate, resources and competition. We applied the model to data on 50 years of annual dates of first flowering by three species of plants in 26 populations covering 4 degrees of latitude in Norway. In agreement with earlier studies, plants in most populations and all three species bloomed earlier following warmer winters. Moreover, our model revealed that earlier blooming reflected increasing influences of resources and density-dependent population limitation under climatic warming. The insights available from the application of this model to phenological data in other taxa will contribute to our understanding of the roles of endogenous versus exogenous processes in the evolution of the timing of life-history events in a changing climate. 相似文献
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Andréia S Lessa Bruno D Paredes Juliana V Dias Adriana B Carvalho Luiz Fernando Quintanilha Christina M Takiya Bernardo R Tura Guilherme FM Rezende Antonio C Campos de Carvalho Célia MC Resende Regina CS Goldenberg 《BMC veterinary research》2010,6(1):1-10
Background
Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Retrospective studies have identified cases predating the initial identification of this form of scrapie, and epidemiological studies have indicated that it does not conform to the behaviour of an infectious disease, giving rise to the hypothesis that it represents spontaneous disease. However, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation in transgenic mice and sheep. The first successful challenge of a sheep with 'field' atypical scrapie from an homologous donor sheep was reported in 2007.Results
This study demonstrates that atypical scrapie has distinct clinical, pathological and biochemical characteristics which are maintained on transmission and sub-passage, and which are distinct from other strains of transmissible spongiform encephalopathies in the same host genotype.Conclusions
Atypical scrapie is consistently transmissible within AHQ homozygous sheep, and the disease phenotype is preserved on sub-passage. 相似文献9.
van Beers JJ Raijmakers R Alexander LE Stammen-Vogelzangs J Lokate AM Heck AJ Schasfoort RB Pruijn GJ 《Arthritis research & therapy》2010,12(6):R219
Introduction
Rheumatoid arthritis (RA) frequently involves the loss of tolerance to citrullinated antigens, which may play a role in pathogenicity. Citrullinated fibrinogen is commonly found in inflamed synovial tissue and is a frequent target of autoantibodies in RA patients. To obtain insight into the B-cell response to citrullinated fibrinogen in RA, its autoepitopes were systematically mapped using a new methodology. 相似文献10.