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排序方式: 共有2110条查询结果,搜索用时 15 毫秒
31.
The effects of deregulation of NR gene expression on growth and nitrogen metabolism of Nicotiana plumbaginifolia plants 总被引:1,自引:0,他引:1
32.
Odile Ozier-Kalogeropoulos Marie-Thérèse Adeline Weng-Lang Yang George M. Carman François Lacroute 《Molecular & general genetics : MGG》1994,242(4):431-439
In the pyrimidine biosynthetic pathway, CTP synthetase catalyses the conversion of uridine 5-triphosphate (UTP) to cytidine 5-triphosphate (CTP). In the yeast Saccharomyces cerevisiae, the URA7 gene encoding this enzyme was previously shown to be nonessential for cell viability. The present paper describes the selection of synthetic lethal mutants in the CTP biosynthetic pathway that led us to clone a second gene, named URA8, which also encodes a CTP synthetase. Comparison of the predicted amino acid sequences of the products of URA7 and URA8 shows 78% identity. Deletion of the URA8 gene is viable in a haploid strain but simultaneous presence of null alleles both URA7 and URA8 is lethal. Based on the codon bias values for the two genes and the intracellular concentrations of CTP in strains deleted for one of the two genes, relative to the wild-type level, URA7 appears to be the major gene for CTP biosynthesis. Nevertheless, URA8 alone also allows yeast growth, at least under standard laboratory conditions. 相似文献
33.
Rinkel Monique Hubert Jean-Claude Roux Brigitte Lett Marie-Claire 《Current microbiology》1994,29(5):249-254
AKlebsiella pneumoniae strain having mobilization helper potential has been isolated from the river Rhine. Analysis of the transconjugants resulting from the mobilization of nonconjugative pBR-type plasmids and RSF1010 derivatives showed that the transfer-helper capacity of theK. pneumoniae strain is related to the presence of a Tn3-like transposable element, Tn5403. This element has been identified and localized in a plasmid. 相似文献
34.
This work was designed to determine the role of the acidity and aluminium stress in the selection of partners in the Acacia symbioses with relevance to the persistence of the microsymbiont Bradyrhizobium in the soil and the growth and nodulation of the host plant respectively. Fifteen strains of Bradyrhizobium from Acacia mangium and Faidherbia albida formed a very homogenous acid tolerant group as indicated by their ability to grow better in a medium at pH 4.5 than in a medium at pH 6.8. By contrast, a growth experiment using an acid liquid media (pH 4.5), containing different concentrations of aluminium successfully identified strains sensitive to aluminium toxicity and those able to grow even in the presence of 100 M AlCl3.Our results suggest that high amounts of aluminium in the soil rather than acidity (pH 4.5) were a major soil factor for selection of Bradyrhizobium strains capable of establishing a permanently high population under natural conditions.Unlike the behaviour of the microsymbiont, growth and nodulation of Acacia mangium and Faidherbia albida were not affected by aluminium, even at 100 M, but they might be significantly affected by medium acidity (pH 4.5) depending on plant provenances. It is therefore suggested that ability of the host plant to tolerate acidity stress should be taken into account first when screening effective Acacia-Bradyrhizobium combinations for use in afforestation trials. 相似文献
35.
The rule of six, a basic feature for efficient replication of Sendai virus defective interfering RNA. 总被引:36,自引:20,他引:16
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The addition of the hepatitis delta virus genomic ribozyme to the 3' end sequence of a Sendai virus defective interfering RNA (DI-H4) allowed the reproducible and efficient replication of this RNA by the viral functions expressed from cloned genes when the DI RNA was synthesized from plasmid. Limited nucleotide additions or deletions (+7 to -7 nucleotides) in the DI RNA sequence were then made at five different sites, and the different RNA derivatives were tested for their abilities to replicate. Efficient replication was observed only when the total nucleotide number was conserved, regardless of the modifications, or when the addition of a total of 6 nucleotides was made. The replicated RNAs were shown to be properly enveloped into virus particles. It is concluded that, to form a proper template for efficient replication, the Sendai virus RNA must contain a total number of nucleotides which is a multiple of 6. This was interpreted as the need for the nucleocapsid protein to contact exactly 6 nucleotides. 相似文献
36.
Mammal Research - Foraging animals must contend with fluctuating environmental variables that affect foraging success, including conditions like wind noise, which could diminish the usefulness of... 相似文献
37.
Karine Cahier Damien Piel Rubén Barcia-Cruz David Goudenège K. Mathias Wegner Marc Monot Jesús L. Romalde Frédérique Le Roux 《Environmental microbiology》2023,25(8):1424-1438
Phages depend on their bacterial hosts to replicate. The habitat, density and genetic diversity of host populations are therefore key factors in phage ecology, but our ability to explore their biology depends on the isolation of a diverse and representative collection of phages from different sources. Here, we compared two populations of marine bacterial hosts and their phages collected during a time series sampling program in an oyster farm. The population of Vibrio crassostreae, a species associated specifically to oysters, was genetically structured into clades of near clonal strains, leading to the isolation of closely related phages forming large modules in phage–bacterial infection networks. For Vibrio chagasii, which blooms in the water column, a lower number of closely related hosts and a higher diversity of isolated phages resulted in small modules in the phage–bacterial infection network. Over time, phage load was correlated with V. chagasii abundance, indicating a role of host blooms in driving phage abundance. Genetic experiments further demonstrated that these phage blooms can generate epigenetic and genetic variability that can counteract host defence systems. These results highlight the importance of considering both the environmental dynamics and the genetic structure of the host when interpreting phage–bacteria networks. 相似文献
38.
This paper describes an experimental investigation concerning the use of neural networks to achieve the non-linear control of a continuous stirred tank fermenter. The influent dilution rate and the substrate concentration have been selected as control variables. The backpropagation learning algorithm has been used for both off-line and on-line identification of the inverse model which provides the control action. Experimental results show the performance and the implementation simplicity of this control approach. 相似文献
39.
40.
Effect of anoxia and reoxygenation on antioxidant enzyme activities in immortalized brain endothelial cells 总被引:1,自引:0,他引:1
Olivier Rabin Michèle Piciotti Katy Drieu Jean-Marie Bourre Françoise Roux 《In vitro cellular & developmental biology. Animal》1996,32(4):221-224
Summary The effects of anoxia and reoxygenation on major antioxidant enzyme activities were investigatedin vitro in immortalized rat brain endothelial cells (RBE4 cells). A sublethal anoxic period of 12 h was assessed for RBE4 cells using the neutral red uptake test. Anoxia markedly influenced the specific activity of catalase and superoxide dismutase,
with no major effect on glutathione peroxidase or glutathione reductase. After 24 h postanoxia, the superoxide dismutase activity
modulated by the presence or absence of oxygen returned to control value.
Damage and recovery of RBE4 immortalized rat brain endothelial cells in culture after exposure to free radicals and other oxygen-derived species provides
a usefulin vitro model to study anoxia-reoxygenation trauma at the cellular level. 相似文献