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  • 1
    Electronic Resource
    Electronic Resource
    A defined sequence within the 3′ UTR of the areA transcript is sufficient to mediate nitrogen metabolite signalling via accelerated deadenylation (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 37 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Nitrogen metabolism in Aspergillus nidulans is regulated by AREA, a member of the GATA family of transcription factors. One mechanism that modulates AREA activity involves the rapid degradation of the areA transcript when sufficient NH4+ or Gln are available. This signalling mechanism has been shown to require a region of 218 nucleotides within the 3′ untranslated region of areA mRNA. We demonstrate that this region functions independently in a heterologous transcript and acts to accelerate degradation of the poly(A) tail, which in turn leads to rapid transcript degradation in response to the addition of NH4+ or Gln to the growth medium. areA transcript degradation is inhibited by cycloheximide, but this is not a general consequence of translational inhibition. We believe that this is the first reported example in which specific physiological signals, acting through a defined sequence within a transcript, have been shown to promote accelerated poly(A) degradation, which in turn triggers transcript degradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.02085.x
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  • 2
    Electronic Resource
    Electronic Resource
    Saccharomyces cerevisiae PAU genes are induced by anaerobiosis (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Saccharomyces cerevisiae PAU genes constitute the largest multigene family in yeast, with 23 members located mainly in subtelomeric regions. The role and regulation of these genes were previously unknown. We detected PAU gene expression during alcoholic fermentation. An analysis of PAU gene regulation using PAU–lacZ fusions and Northern analyses revealed that they were regulated by anaerobiosis. PAU genes display, however, different abilities to be induced by anaerobiosis and this appears to be related to their chromosomal localization; two subtelomeric copies are more weakly inducible than an interstitial one. We show that PAU genes are negatively regulated by oxygen and repressed by haem. Examination of PAU gene expression in rox1Δ and tup1Δ strains indicates that PAU repression by oxygen is mediated by an unknown, haem-dependent pathway, which does not involve the Rox1p anaerobic repressor but requires Tup1p. Given the size of the gene family, PAU genes could be expected to be important during yeast life and some of them probably help the yeast to cope with anaerobiosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01807.x
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  • 3
    Electronic Resource
    Electronic Resource
    Correlations between nutrient concentrations and zooplankton populations in a mesotrophic reservoir (2002)
    Oxford UK : Blackwell Science Ltd
    Freshwater biology 47 (2002), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. A year-round study was conducted in a mesotrophic reservoir to determine the dynamics of zooplankton populations as a function of food availability (edible phytoplankton), nutrient concentration, temperature and hydraulic regime.2. Rotifer biomass was correlated with soluble reactive phosphorus (SRP) concentration. The abundance of the rotifers Keratella cochlearis and Anuraeopsis fissa were not correlated with food availability (measured by chlorophyll and cell counts) but showed a strong dependence on P availability. Another rotifer, Synchaeta oblonga, and crustacean species were not related to nutrient availability but seemed to be dependent on food concentrations, especially of some phytoplankton taxa.3. In this field study, rotifers seemed more susceptible than Daphnia or copepods to P-limitation. Among rotifer species, Keratella seemed to be more susceptible than Anuraeopsis to P limitation. Different susceptibilities of zooplankton species to nutrient limitation may be important in explaining the dynamics of these organisms in natural situations. Further analyses are warranted to clarify the interactions between nutrient limitation and energy limitation among zooplankton.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2002.00882.x
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  • 4
    Electronic Resource
    Electronic Resource
    Reproduction of interspecific hybrids of Atlantic salmon and brown trout in a stream environment (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Reproduction between Atlantic salmon males and interspecific hybrid Salmo salar × Salmo trutta females was monitored in a controlled flow channel diverted from a south European river located at the edge of Atlantic salmon natural geographic distribution in Europe.2. Post-F1 hybrids were viable and survived in the wild, at least until dispersal from redds. After transfer to hatchery conditions, 67% survived into the second year.3. The hybrids possessed 98 chromosomes: two sets of Atlantic salmon(2n = 58) and one set of brown trout (n = 40) chromosomes.4. The existence of a low proportion of allotriploid individuals can be expected in rivers where Atlantic salmon and brown trout populations coexist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01068.x
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  • 5
    Electronic Resource
    Electronic Resource
    Chemical composition and construction cost for roots of Mediterranean trees, shrub species and grassland communities (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The construction cost of fine roots was studied in 23 woody species and two grassland communities, growing under natural conditions in southern Spain. Calculation of the energy (glucose) required for their synthesis was based on the quantification of chemical components present in tissues. Despite considerable differences in the chemical composition of the three life forms studied (trees, shrubs and herbaceous), detected differences in construction cost were non-significant (mean value: 1·64 ± 0·13 g glucose g−1). However, shrubs and herbaceous plants growing in more fertile habitats expended significantly less energy on root synthesis (1·58 ± 0·06 and 1·41 ± 0·05 g glucose g−1, respectively) than those growing in less fertile areas (1·80 ± 0·06 and 1·57 ± 0·1 g glucose g−1, respectively), because they contained smaller amounts of either waxes (shrubs) or lignins (herbaceous), both expensive to synthesize, and, proportionately, more cellulose; which is inexpensive to synthesize. Deciduous and evergreen tree species also differed mainly with regard to wax and cellulose contents, giving rise to a significantly higher construction cost in evergreens (1·57 ± 0·07 g glucose g−1 versus 1·78 ± 0·02 g glucose g−1). The differences observed in construction cost appeared to be due more to habitat-induced differences in chemical composition than to any intrinsic difference between the species studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00848.x
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  • 6
    Electronic Resource
    Electronic Resource
    Root respiration and associated costs in deciduous and evergreen species of Quercus (2002)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Root construction and maintenance costs were estimated in four evergreen and three deciduous Quercus species that are typical in the landscape of southern Spain. The cost quantification was based on analysis of the growth–­respiration ratio. Values observed for both construction cost (ranging from 1·17 to 1·29 g glucose g−1 dry weight) and maintenance   cost   (ranging   from   6·22   to   11·71 mg glucose g−1 dry weight d−1) were generally lower than those reported in other studies. The results showed non-significant differences between deciduous and evergreen species. The lack of significant differences between species appeared to be due to the homogeneity of growth conditions. Hydroponic culture, with unrestricted nutrient and water supply, would lead to low tissue carbon content and low respiration rates, leading to the low costs observed. Furthermore, the fact that root organs are clearly importers of organic molecules inevitably entails some underestimation of the respiration associated with growth and, to a lesser extent, with maintenance respiration. This leads in turn to underestimation of the corresponding construction and maintenance costs. All this raises doubts as to the suitability of this method for studying root systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00903.x
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  • 7
    Electronic Resource
    Electronic Resource
    Assessing introgression of foreign strains in wild Atlantic salmon populations: variation in microsatellites assessed in historic scale collections (2001)
    Oxford UK : Blackwell Science Ltd
    Freshwater biology 46 (2001), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Genetic variation at five microsatellite loci was analysed in a collection of scales (1970–97) sampled from Atlantic salmon adults returning to the Nivelle River (South France).2. Native and foreign fish (from an allochthonous Scottish stock introduced into the river to increase population size) were clearly identified as all foreign individuals released in the river were physically marked.3. Introgression of foreign genes into the native gene pool has occurred, although the reproductive success of foreign Atlantic salmon in the wild was lower than that of native individuals.4. The utility of old scale samples for investigating the impact of foreign stocking on wild fish populations is demonstrated in this work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2001.00711.x
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  • 8
    Electronic Resource
    Electronic Resource
    Characterization of nitrogen metabolite signalling in Aspergillus via the regulated degradation of areA mRNA (2001)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 42 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: AreA is the principal transcription factor involved in determining nitrogen utilization in Aspergillus nidulans. NH4+ and Gln are utilized preferentially but in their absence, AreA acts to facilitate the expression of genes involved in metabolizing alternative nitrogen sources. It is crucial to the function of AreA that its expression is tightly modulated by the quality and availability of nitrogen sources. One signalling mechanism involves regulated degradation of the areA transcript in response to NH4+ and Gln, which provides the first direct means of monitoring nitrogen signalling in this fungus. Here we assess the specificity of the transcript degradation response, determining that it responds qualitatively to a variety of additional nitrogen sources including Asn. Furthermore, the response to Gln and NH4+ requires the same discrete region of the areA 3′-UTR but both NH4+ and Asn need to be metabolized to Gln before they are effective as a signal. However, NH4+ signalling is independent of AreA activity, unlike Gln and Asn signalling. A mutation in the structural gene for NADP-linked glutamate dehydrogenase, gdhA, which disrupts metabolism of NH4+ to Glu, is additive with mutations in two distinct regions of areA that disrupt the previously identified signalling mechanisms. The triple mutant is both strongly derepressed and expresses very high levels of nitrate reductase activity. These data suggest nitrogen metabolism in A. nidulans is in part regulated in response to the intracellular levels of Gln via the regulated degradation of areA mRNA, but the intracellular Gln level is not the sole determinant of nitrogen metabolite repression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02636.x
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  • 9
    Electronic Resource
    Electronic Resource
    The role of the yeast plasma membrane SPS nutrient sensor in the metabolic response to extracellular amino acids (2001)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 42 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In response to discrete environmental cues, Saccharomyces cerevisiae cells adjust patterns of gene expression and protein activity to optimize metabolism. Nutrient-sensing systems situated in the plasma membrane (PM) of yeast have only recently been discovered. Ssy1p is one of three identified components of the Ssy1p–Ptr3p–Ssy5 (SPS) sensor of extracellular amino acids. SPS sensor-initiated signals are known to modulate the expression of a number of amino acid and peptide transporter genes (i.e. AGP1, BAP2, BAP3, DIP5, GAP1, GNP1, TAT1, TAT2 and PTR2) and arginase (CAR1). To obtain a better understanding of how cells adjust metabolism in response to extracellular amino acids in the environment and to assess the consequences of loss of amino acid sensor function, we investigated the effects of leucine addition to wild-type and ssy1 null mutant cells using genome-wide transcription profile analysis. Our results indicate that the previously identified genes represent only a subset of the full spectrum of Ssy1p-dependent genes. The expression of several genes encoding enzymes in amino acid biosynthetic pathways, including the branched-chain, lysine and arginine, and the sulphur amino acid biosynthetic pathways, are modulated by Ssy1p. Additionally, the proper transcription of several nitrogen-regulated genes, including NIL1 and DAL80, encoding well-studied GATA transcription factors, is dependent upon Ssy1p. Finally, several genes were identified that require Ssy1p for wild-type expression independently of amino acid addition. These findings demonstrate that yeast cells require the SPS amino acid sensor component, Ssy1p, to adjust diverse cellular metabolic processes properly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02627.x
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  • 10
    Electronic Resource
    Electronic Resource
    Homing of a bacterial group II intron with an intron-encoded protein lacking a recognizable endonuclease domain (2000)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 35 (2000), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: RmInt1 is a functional group II intron found in Sinorhizobium meliloti where it interrupts a group of IS elements of the IS630-Tc1 family. In contrast to many other group II introns, the intron-encoded protein (IEP) of RmInt1 lacks the characteristic conserved part of the Zn domain associated with the IEP endonuclease activity. Nevertheless, in this study, we show that RmInt1 is capable of inserting into a vector containing the DNA spanning the RmInt1 target site from the genome of S. meliloti. Efficient homing was also observed in the absence of homologous recombination (RecA− strains). In addition, it is shown that RmInt1 is able to move to its target in a heterologous host (S. medicae). Homing of RmInt1 occurs very efficiently upon DNA target uptake (conjugation/electroporation) by the host cell resulting in a proportion of invaded target of 11–30%. Afterwards, the remaining intronless target DNA is protected from intron invasion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2000.01804.x
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