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By chemoenzymatic synthesis the gene for a (Leu27) analogue of human growth hormone releasing hormone-Gly45 [(Leu27)GHRH-Gly45] was constructed, cloned and expressed in Escherichia coli as a fusion protein with beta-galactosidase under the control of the lac promoter and operator. Upon induction with isopropyl-D-thio-beta-galactopyranoside the fusion protein accumulated to a yield of 15-20% of the total cellular protein. After cyanogen bromide cleavage of the fusion protein the precursor peptide (Leu27)hGHRH-Gly45 was separated by extraction and purified by ion exchange and h.p.l.c.-RP18 chromatography. The purified peptide was analysed by sequencing, isoelectric focusing, amino acid analysis and amino acid analysis after V8 protease digestion. The carboxy-terminal glycine was subsequently amidated by PAM (peptidylglycine-alpha-amidating-monooxygenase), an enzyme which was isolated and characterized from fresh bovine pituitaries. Correct amidation of the penultimate amino acid, leucine, was verified by peptide sequencing with an authentic leucine amide reference. 相似文献
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W R Engels 《BioEssays : news and reviews in molecular, cellular and developmental biology》1992,14(10):681-686
The P family of transposable genetic elements is thought to be a recent addition to the Drosophila melanogaster genome. New evidence suggests that the elements came from another Drosophila species, possibly carried by parasitic mites. The transposition mechanism of P elements involves DNA gap repair which may have facilitated their rapid spread through D. melanogaster worldwide. These results provide new insight into the process of a transposon's invasion into a new species and the potential risk of extinction such an invasion might entail. 相似文献
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Diastereomeric dinucleoside-methylphosphonates: determination of configuration with the 2-D NMR ROESY technique. 总被引:5,自引:5,他引:0 下载免费PDF全文
The determination of configuration at phosphorus in diastereomeric dinucleoside-methylphosphonates having the -O-P(= O)(-CH3)-O- internucleotide linkage with the NOE derived ROESY NMR technique is described for ApT, TpT, ApA, TpA and CpG. For this purpose ROE's from the P-CH3 group to the protons in the nearest neighbourhood were measured. These ROE's are different within diastereomeric pairs of a dimer enabling us to deduce the individual configuration. The validity of the method is proven in comparison with dimers of known configuration (ApT, TpT). Together with a recently published diastereoselective synthesis method a more homogeneous picture between physical properties and the corresponding configuration is provided. There is an improvement in our knowledge about the stereochemistry of these substances which could not be deduced from the data known before. 相似文献
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During prolonged cultivation of S. aureus strains 104 and NCTC 8178 in continuous culture, staphylocoagulase-negative mutants arose and accumulated progressively in increasing proportions. The resulting loss of production of staphylocoagulase was accompanied by a simultaneous loss of production of -haemolysin and PV-leucocidin. Characterization of the strains revealed no further differences in biotype, exoenzymes, phage pattern and plasmid content.Cultivation in batch cultures showed that the maximal specific growth rates and specific oxygen-consumption rates of the mutant strains were slightly higher than those of the parent strains, whereas the production of total extracellular protein of the mutant strains had decreased significantly.From competition experiments between parent and mutant strains in chemostat cultures at different dilution rates and cultivation temperatures, it was concluded that the underlying mechanism of accumulation of staphylocoagulase-negative mutants in the chemostat is based on differences in affinity for the limiting substrate(s) rather than on differences in the production rates of total extracellular proteins. The complete repression of three exoenzymes, a partial repression of the total extracellular protein production, and an increased affinity for the limiting substrate(s) suggested that a mutation in a regulatory gene is involved. The possible role of a transposon in this mutation is discussed. 相似文献
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Eric Allan Wolfgang W. Weisser Markus Fischer Ernst-Detlef Schulze Alexandra Weigelt Christiane Roscher Jussi Baade Romain L. Barnard Holger Beßler Nina Buchmann Anne Ebeling Nico Eisenhauer Christof Engels Alexander J. F. Fergus Gerd Gleixner Marlén Gubsch Stefan Halle Alexandra M. Klein Ilona Kertscher Annely Kuu Markus Lange Xavier Le Roux Sebastian T. Meyer Varvara D. Migunova Alexandru Milcu Pascal A. Niklaus Yvonne Oelmann Esther Pašalić Jana S. Petermann Franck Poly Tanja Rottstock Alexander C. W. Sabais Christoph Scherber Michael Scherer-Lorenzen Stefan Scheu Sibylle Steinbeiss Guido Schwichtenberg Vicky Temperton Teja Tscharntke Winfried Voigt Wolfgang Wilcke Christian Wirth Bernhard Schmid 《Oecologia》2013,173(1):223-237
In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination. 相似文献
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Simone Caroline Cappellari Birgit Harter-Marques Pia Aumeier Wolf Engels 《Biotropica》2009,41(6):721-729
Floral characteristics often indicate the pollinators' functional group visiting the plant and the pollination syndromes associated with them. This idea has been challenged in the past decades due to increasing evidence that most plants, including those exhibiting floral syndromes, are visited by large arrays of species that differ in their effectiveness as pollinators. Our study focuses on Mecardonia tenella (Plantaginaceae) from the Araucaria forest of southern Brazil, which exhibits characteristics of the oil flower pollination syndrome. However, it is visited by three types of functional groups of bees: male orchid bees, oil-collecting bees, and pollen-seeking bees. The relative contribution of each functional group to the plant's reproductive success was estimated based on their pollen load, visitation frequency, and morphology. We assessed resources, phenology, and breeding system of M. tenella . Our results indicate that flowers lack nectar, but volatiles, lipids, and pollen are resources that can be gathered by visitors. This combination of floral traits and visitors' assemblage makes M. tenella a challenge to the concept of pollination syndromes. Our findings indicate that the current interactions may not reflect the circumstances under which some floral traits of this plant were selected. 相似文献
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A critical role for tetraspanin CD151 in alpha3beta1 and alpha6beta4 integrin-dependent tumor cell functions on laminin-5 下载免费PDF全文
Winterwood NE Varzavand A Meland MN Ashman LK Stipp CS 《Molecular biology of the cell》2006,17(6):2707-2721
The basement membrane protein laminin-5 supports tumor cell adhesion and motility and is implicated at multiple steps of the metastatic cascade. Tetraspanin CD151 engages in lateral, cell surface complexes with both of the major laminin-5 receptors, integrins alpha3beta1 and alpha6beta4. To determine the role of CD151 in tumor cell responses to laminin-5, we used retroviral RNA interference to efficiently silence CD151 expression in epidermal carcinoma cells. Near total loss of CD151 had no effect on steady state cell surface expression of alpha3beta1, alpha6beta4, or other integrins with which CD151 associates. However, CD151-silenced carcinoma cells displayed markedly impaired motility on laminin-5, accompanied by unusually persistent lateral and trailing edge adhesive contacts. CD151 silencing disrupted alpha3beta1 integrin association with tetraspanin-enriched microdomains, reduced the bulk detergent extractability of alpha3beta1, and impaired alpha3beta1 internalization in cells migrating on laminin-5. Both alpha3beta1- and alpha6beta4-dependent cell adhesion to laminin-5 were also impaired in CD151-silenced cells. Reexpressing CD151 in CD151-silenced cells reversed the adhesion and motility defects. Finally, loss of CD151 also impaired migration but not adhesion on substrates other than laminin-5. These data show that CD151 plays a critical role in tumor cell responses to laminin-5 and reveal promotion of integrin recycling as a novel potential mechanism whereby CD151 regulates tumor cell migration. 相似文献