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991.
992.
993.
Dozol H Maechling C Graff R Matsuda A Shuto S Spiess B 《Biochimica et biophysica acta》2004,1671(1-3):1-8
Four adenophostin analogues lacking the adenine moiety were subjected to 31P- and 1H-NMR titrations in order to determine the acid-base behaviour of the individual ionisable groups of the molecules and the complex interplay of intramolecular interactions resulting from the protonation process. For the two trisphosphorylated compounds, the curve pattern of the phosphorus nuclei corresponds to the superimposition of the titration curves of a monophosphorylated polyol and a polyol carrying two vicinal phosphates, suggesting that the two phosphate moieties behave independently. Also, the general shape of 1H-NMR titration curves of the studied compounds is very close to that of adenophostin A, indicating that the adenine moiety does not specifically interact with the phosphorylated sugar moieties. The curves show, however, that both trisphosphorylated compounds adopt slightly different preferential conformations which could contribute to explain the difference in their affinity for Ins(1,4,5)P3 receptor. Their macroscopic as well as the microscopic protonation constants are higher than those of adenophostin A, indicating that the adenine moiety plays a base-weakening effect on the phosphate groups. Further analysis of the microscopic protonation constants confirms that the compound whose conformation is the closest to that of adenophostin A also shows the highest biological activity. The two bisphosphorylated analogues studied behave very similarly, suggesting that the deletion of the hydroxymethyl group on the pentafuranosyl ring only weakly influences the protonation process of the phosphate groups that bear the glucopyranose moiety. 相似文献
994.
Crystal T. Engineer Claudia A. Perez Ryan S. Carraway Kevin Q. Chang Jarod L. Roland Andrew M. Sloan Michael P. Kilgard 《PloS one》2013,8(10)
Humans and animals readily generalize previously learned knowledge to new situations. Determining similarity is critical for assigning category membership to a novel stimulus. We tested the hypothesis that category membership is initially encoded by the similarity of the activity pattern evoked by a novel stimulus to the patterns from known categories. We provide behavioral and neurophysiological evidence that activity patterns in primary auditory cortex contain sufficient information to explain behavioral categorization of novel speech sounds by rats. Our results suggest that category membership might be encoded by the similarity of the activity pattern evoked by a novel speech sound to the patterns evoked by known sounds. Categorization based on featureless pattern matching may represent a general neural mechanism for ensuring accurate generalization across sensory and cognitive systems. 相似文献
995.
Hlne Chabas Viktor Müller Sebastian Bonhoeffer Roland R. Regoes 《PLoS computational biology》2022,18(7)
Bacteria have adaptive immunity against viruses (phages) in the form of CRISPR-Cas immune systems. Currently, 6 types of CRISPR-Cas systems are known and the molecular study of three of these has revealed important molecular differences. It is unknown if and how these molecular differences change the outcome of phage infection and the evolutionary pressure the CRISPR-Cas systems faces. To determine the importance of these molecular differences, we model a phage outbreak entering a population defending exclusively with a type I/II or a type III CRISPR-Cas system. We show that for type III CRISPR-Cas systems, rapid phage extinction is driven by the probability to acquire at least one resistance spacer. However, for type I/II CRISPR-Cas systems, rapid phage extinction is characterized by an a threshold-like behaviour: any acquisition probability below this threshold leads to phage survival whereas any acquisition probability above it, results in phage extinction. We also show that in the absence of autoimmunity, high acquisition rates evolve. However, when CRISPR-Cas systems are prone to autoimmunity, intermediate levels of acquisition are optimal during a phage outbreak. As we predict an optimal probability of spacer acquisition 2 factors of magnitude above the one that has been measured, we discuss the origin of such a discrepancy. Finally, we show that in a biologically relevant parameter range, a type III CRISPR-Cas system can outcompete a type I/II CRISPR-Cas system with a slightly higher probability of acquisition. 相似文献
996.
Fritsch RM Schneider G Saur D Scheibel M Schmid RM 《The Journal of biological chemistry》2007,282(31):22551-22562
The integrated stress response (ISR) integrates a broad range of environmental and endogenous stress signals to the phosphorylation of the alpha-subunit of eukaryotic translation initiation factor 2 (eIF2 alpha). Although intense or prolonged activation of this pathway is known to induce apoptosis, the molecular mechanisms coupling stress-induced eIF2 alpha phosphorylation to the cell death machinery have remained incompletely understood. In this study, we characterized apoptosis initiation in response to classical activators of the ISR (tunicamycin, UVC, elevated osmotic pressure, arsenite). We found that all applied stress stimuli activated a mitochondrial pathway of apoptosis initiation. Rapid and selective down-regulation of the anti-apoptotic BCL-2 family protein MCL-1 preceded the activation of BAX, BAK, and caspases. Stabilization of MCL-1 blocked apoptosis initiation, while cells with reduced MCL-1 protein content were strongly sensitized to stress-induced apoptosis. Stress-induced elimination of MCL-1 occurred with unchanged protein turnover and independently of MCL-1 mRNA levels. In contrast, stress-induced phosphorylation of eIF2 alpha at Ser(51) was both essential and sufficient for the down-regulation of MCL-1 protein in stressed cells. These findings indicate that stress-induced phosphorylation of eIF2 alpha is directly coupled to mitochondrial apoptosis regulation via translational repression of MCL-1. Down-regulation of MCL-1 enables but not enforces apoptosis initiation in stressed cells. 相似文献
997.
Forecasting Environmental Responses to Restoration of Rivers Used as Log Floatways: An Interdisciplinary Challenge 总被引:1,自引:0,他引:1
Christer Nilsson Fabio Lepori Björn Malmqvist Erik Törnlund Niclas Hjerdt James M. Helfield Daniel Palm Johan Östergren Roland Jansson Eva Brännäs Hans Lundqvist 《Ecosystems》2005,8(7):779-800
Log floating in the 19th to mid 20th centuries has profoundly changed the environmental conditions in many northern river
systems of the world. Regulation of flow by dams, straightening and narrowing of channels by various piers and wing dams,
and homogenization of bed structure are some of the major impacts. As a result, the conditions for many riverine organisms
have been altered. Removing physical constructions and returning boulders to the channels can potentially restore conditions
for these organisms. Here we describe the history of log driving, review its impact on physical and biological conditions
and processes, and predict the responses to restoration. Reviewing the literature on comparable restoration efforts and building
upon this knowledge, using boreal Swedish rivers as an example, we address the last point. We hypothesize that restoration
measures will make rivers wider and more sinuous, and provide rougher bottoms, thus improving land-water interactions and
increasing the retention capacity of water, sediment, organic matter and nutrients. The geomorphic and hydraulic/hydrologic
alterations are supposed to favor production, diversity, migration and reproduction of riparian and aquatic organisms. The
response rates are likely to vary according to the types of processes and organisms. Some habitat components, such as beds
of very large boulders and bedrock outcrops, and availability of sediment and large woody debris are believed to be extremely
difficult to restore. Monitoring and evaluation at several scales are needed to test our predictions. 相似文献
998.
John G. Day Erica E. Benson Roland A. Fleck 《In vitro cellular & developmental biology. Plant》1999,35(2):127-136
Summary Microalgae are a highly diverse group of unicellular organisms comprising the eukaryotic protists and the prokaryotic cyanobacteria
or blue-green algae. The microalgae have a unique environmental status; being virtually ubiquitous in euphotic aquatic niches,
they can occupy extreme habitats ranging from tropical coral reefs to the polar regions, and they contribute to half of the
globe’s photosynthetic activity. Furthermore, they form the basis of the food chain for more than 70% of the world’s biomass.
Microalgae are a valuable environmental and biotechnological resource, and the aim of this review is to explore the use of
in vitro technologies in the conservation and sustainable exploitation of this remarkable group of organisms. The first part
of the review evaluates the importance of in vitro methods in the maintenance and conservation of microalgae and describes
the central role of culture collections in applied algal research. The second part explores the application of microalgal
in vitro technologies, particularly in the context of the aquaculture and biotechnology industries. Emphasis is placed upon
the exploitation of economically important algal products including aquaculture feed, biomass production for the health care
sector, green fertilizers, pigments, vitamins, antioxidants, and antimicrobial agents. The contribution that microalgae can
make to environmental research is also appraised; for example, they have an important role as indicator organisms in environmental
impact assessments. Similarly, designated culture collection strains of microalgae are used for ecotoxicity testing. Throughout
the review, emphasis is placed on the application of in vitro techniques for the continued advancement of microalgal research.
The paper concludes by assessing future perspectives for the novel application of microalgae and their products. 相似文献
999.
Fabrice Rebeille Richard Bligny Roland Douce 《Archives of biochemistry and biophysics》1982,219(2):371-378
In view of the importance of Pi in the control of cell metabolism, it was of interest to study the mechanism and regulation of Pi uptake by Acer pseudoplatanus cells grown as cell suspensions. At low external Pi concentrations up to 10 mm, sycamore cells incorporate phosphate against a concentration gradient, by a process which is energy dependent. Under these conditions the intracellular Pi concentration is maintained constant (2–3 mm). On the contrary at high external Pi concentrations, higher than that which counterpoises the cytoplasmic Pi concentration (approximately 10 mm), Pi enters the cell by slow diffusion and the intracellular Pi concentration increases continuously as the extracellular Pi concentration increases from 15 to 50 mm. When sycamore cells are transferred to a phosphate-deficient medium, growth slows down considerably and ceases after 4–5 days. During this time, intracellular Pi concentration falls from 3 to 0.1 mm and phosphate esters from 8 to 2 mm. Phosphate starvation stimulates the uptake indicating that phosphate uptake depends on the intracellular phosphate and/or cytoplasmic ester-P pool. Pi uptake by Pi-starved cells is strongly dependent on the pH of the medium. 相似文献
1000.
Douglas B. Vasey C. Roland Wolf Ken Brown C. Bruce A. Whitelaw 《Transgenic research》2011,20(1):23-28
Throughout development cells make the decision to proliferate, arrest or die. Control of this process is essential for normal
development, with unrestrained cell proliferation and cell death underling the origin and progression of disease. The cell-cycle
is tightly regulated by a number of factors including the cyclin-dependent kinase inhibitor 1A (Cdkn1a), termed p21 (or Cip1
or WAF1). p21 acts as a negative regulator of cell-cycle progression by binding and inhibiting complexes formed between the
cyclin-dependent kinases and their catalytic partners the cyclins. In this report we identify the temporal spatial expression
profile of p21 in the developing mid-term mouse embryo using a p21-LacZ reporter mouse line. Expression of p21 was restricted
to specific regions with a correspondence to both areas of terminal differentiation and active remodelling. A complex temporal
and spatial relationship between p21 expression and regions of apoptosis was evident. A protective role with regard to apoptosis
for p21 is proposed. 相似文献