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排序方式: 共有329条查询结果,搜索用时 62 毫秒
221.
Amino acid sequence of Cro regulatory protein of bacteriophage lambda 总被引:18,自引:0,他引:18
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Raxworthy CJ Martinez-Meyer E Horning N Nussbaum RA Schneider GE Ortega-Huerta MA Townsend Peterson A 《Nature》2003,426(6968):837-841
Despite the importance of tropical biodiversity, informative species distributional data are seldom available for biogeographical study or setting conservation priorities. Modelling ecological niche distributions of species offers a potential solution; however, the utility of old locality data from museums, and of more recent remotely sensed satellite data, remains poorly explored, especially for rapidly changing tropical landscapes. Using 29 modern data sets of environmental land coverage and 621 chameleon occurrence localities from Madagascar (historical and recent), here we demonstrate a significant ability of our niche models in predicting species distribution. At 11 recently inventoried sites, highest predictive success (85.1%) was obtained for models based only on modern occurrence data (74.7% and 82.8% predictive success, respectively, for pre-1978 and all data combined). Notably, these models also identified three intersecting areas of over-prediction that recently yielded seven chameleon species new to science. We conclude that ecological niche modelling using recent locality records and readily available environmental coverage data provides informative biogeographical data for poorly known tropical landscapes, and offers innovative potential for the discovery of unknown distributional areas and unknown species. 相似文献
225.
Group I metabotropic glutamate receptors (consisting of mGluR1 and mGluR5) are G-protein-coupled neurotransmitter receptors that are found in the perisynaptic region of the postsynaptic membrane. These receptors are not activated by single synaptic volleys but rather require bursts of activity. They are implicated in many forms of neural plasticity including hippocampal long-term potentiation and depression, cerebellar long-term depression, associative learning, and cocaine addiction. When activated, group I mGluRs engage two G-protein-dependent signalling mechanisms: stimulation of phospholipase C and activation of an unidentified, mixed-cation excitatory postsynaptic conductance (EPSC), displaying slow activation, in the plasma membrane. Here we report that the mGluR1-evoked slow EPSC is mediated by the TRPC1 cation channel. TRPC1 is expressed in perisynaptic regions of the cerebellar parallel fibre-Purkinje cell synapse and is physically associated with mGluR1. Manipulations that interfere with TRPC1 block the mGluR1-evoked slow EPSC in Purkinje cells; however, fast transmission mediated by AMPA-type glutamate receptors remains unaffected. Furthermore, co-expression of mGluR1 and TRPC1 in a heterologous system reconstituted a mGluR1-evoked conductance that closely resembles the slow EPSC in Purkinje cells. 相似文献
226.
Caudy AA Ketting RF Hammond SM Denli AM Bathoorn AM Tops BB Silva JM Myers MM Hannon GJ Plasterk RH 《Nature》2003,425(6956):411-414
RNA interference (RNAi) regulates gene expression by the cleavage of messenger RNA, by mRNA degradation and by preventing protein synthesis. These effects are mediated by a ribonucleoprotein complex known as RISC (RNA-induced silencing complex). We have previously identified four Drosophila components (short interfering RNAs, Argonaute 2 (ref. 2), VIG and FXR) of a RISC enzyme that degrades specific mRNAs in response to a double-stranded-RNA trigger. Here we show that Tudor-SN (tudor staphylococcal nuclease)--a protein containing five staphylococcal/micrococcal nuclease domains and a tudor domain--is a component of the RISC enzyme in Caenorhabditis elegans, Drosophila and mammals. Although Tudor-SN contains non-canonical active-site sequences, we show that purified Tudor-SN exhibits nuclease activity similar to that of other staphylococcal nucleases. Notably, both purified Tudor-SN and RISC are inhibited by a specific competitive inhibitor of micrococcal nuclease. Tudor-SN is the first RISC subunit to be identified that contains a recognizable nuclease domain, and could therefore contribute to the RNA degradation observed in RNAi. 相似文献
227.
Multiple specificity of thrombin for synthetic substrates 总被引:1,自引:0,他引:1
228.
Molecular basis of osteoarthritis: biomechanical aspects 总被引:5,自引:0,他引:5
Kerin A Patwari P Kuettner K Cole A Grodzinsky A 《Cellular and molecular life sciences : CMLS》2002,59(1):27-35
The unique biomechanical properties of healthy cartilage ensure that articular cartilage is able to transmit force between
the joints while maintaining almost friction-free limb movement. In osteoarthritis, the biomechanical properties are compromised,
but we still do not understood whether this precedes the onset of the disease or is a result of it. This review focuses on
the physical changes to cartilage with age, disease, and mechanical loading, with specific reference to the increased collagen
cross-linking that occurs with age (nonenzymatic glycation), and the response of chondrocytes to physiological and pathological
loads. In addition, the biomechanical properties and matrix biosynthesis of cartilage from various joint surfaces of the knee
and ankle are compared to elucidate reasons why the ankle is less affected by progressive osteoarthritis than the knee. 相似文献
229.
Dissecting the architecture of a quantitative trait locus in yeast 总被引:28,自引:0,他引:28
Steinmetz LM Sinha H Richards DR Spiegelman JI Oefner PJ McCusker JH Davis RW 《Nature》2002,416(6878):326-330
Most phenotypic diversity in natural populations is characterized by differences in degree rather than in kind. Identification of the actual genes underlying these quantitative traits has proved difficult. As a result, little is known about their genetic architecture. The failures are thought to be due to the different contributions of many underlying genes to the phenotype and the ability of different combinations of genes and environmental factors to produce similar phenotypes. This study combined genome-wide mapping and a new genetic technique named reciprocal-hemizygosity analysis to achieve the complete dissection of a quantitative trait locus (QTL) in Saccharomyces cerevisiae. A QTL architecture was uncovered that was more complex than expected. Functional linkages both in cis and in trans were found between three tightly linked quantitative trait genes that are neither necessary nor sufficient in isolation. This arrangement of alleles explains heterosis (hybrid vigour), the increased fitness of the heterozygote compared with homozygotes. It also demonstrates a deficiency in current approaches to QTL dissection with implications extending to traits in other organisms, including human genetic diseases. 相似文献
230.
Post-translational disruption of dystroglycan-ligand interactions in congenital muscular dystrophies 总被引:24,自引:0,他引:24
Michele DE Barresi R Kanagawa M Saito F Cohn RD Satz JS Dollar J Nishino I Kelley RI Somer H Straub V Mathews KD Moore SA Campbell KP 《Nature》2002,418(6896):417-422
Muscle eye brain disease (MEB) and Fukuyama congenital muscular dystrophy (FCMD) are congenital muscular dystrophies with associated, similar brain malformations. The FCMD gene, fukutin, shares some homology with fringe-like glycosyltransferases, and the MEB gene, POMGnT1, seems to be a new glycosyltransferase. Here we show, in both MEB and FCMD patients, that alpha-dystroglycan is expressed at the muscle membrane, but similar hypoglycosylation in the diseases directly abolishes binding activity of dystroglycan for the ligands laminin, neurexin and agrin. We show that this post-translational biochemical and functional disruption of alpha-dystroglycan is recapitulated in the muscle and central nervous system of mutant myodystrophy (myd) mice. We demonstrate that myd mice have abnormal neuronal migration in cerebral cortex, cerebellum and hippocampus, and show disruption of the basal lamina. In addition, myd mice reveal that dystroglycan targets proteins to functional sites in brain through its interactions with extracellular matrix proteins. These results suggest that at least three distinct mammalian genes function within a convergent post-translational processing pathway during the biosynthesis of dystroglycan, and that abnormal dystroglycan-ligand interactions underlie the pathogenic mechanism of muscular dystrophy with brain abnormalities. 相似文献