bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peptide‐mediated macrolide resistance reveals possible specific interactions in the nascent peptide exit tunnel
Authors: Vimberg Vladimir , Xiong Liqun , Bailey Marne , Tenson Tanel , Mankin Alexander 
Published: October 2004

SummaryExpression of specific short peptides can render cells resistant to macrolide antibiotics. Peptides conferring resistance to structurally different macrolides including oleandomycin, azithromycin, azaerythromycin, josamycin and a ketolide cethromycin were selected from a random pentapeptide expression library. Analysis of the entire collection of the resistance peptides allowed their classification into five distinct groups according to their sequence similarity and the type of resistance they confer. A strong correlation was observed between the structures of macrolide antibiotics and sequences of the peptides conferring resistance. Such a correlation indicates that sequence‐specific interactions between the nascent peptide and the macrolide antibiotic and/or the ribosome can occur in the ribosomal exit tunnel.
Activation of the RcsC/YojN/RcsB phosphorelay system attenuates Salmonella virulence
Authors: Mouslim Chakib , Delgado Mónica , Groisman Eduardo A. 
Published: October 2004

SummaryBacterial pathogens have the ability to sense their presence in host tissues and to promote expression of their virulence factors in a time‐ and location‐dependent manner. However, little is known about those genes whose expression is detrimental and thus suppressed during infection. Here we report that constitutive activation of the RcsC/YojN/RcsB system resulting from a mutation in the rcsC sensor gene dramatically attenuates Salmonella virulence. Mutation of the cognate response regulator gene rcsB restored full virulence to the rcsC constitutive mutant, indicating that virulence attenuation results from aberrant expression of RcsB‐regulated genes. The virulence attenuation phenotype was partially dependent on the regulatory gene rcsA, which is necessary for transcription of certain RcsB‐regulated genes, and on the RcsB‐ and RcsA‐dependent colanic acid capsule synthesis cps operon. The rcsC constitutive mutant was phagocytized less efficiently by macrophages and it was defective for invasion of non‐phagocytic cells and survival within macrophages; but it could protect mice upon challenge with wild‐type Salmonella. Our results suggest that a successful infection demands that pathogens turn off expression of products that might interfere with virulence functions.
Modulation of AraC family member activity by protein ligands
Authors: Plano Gregory V. 
Published: October 2004

SummaryA number of AraC family transcriptional activators bind low‐molecular‐weight ligands that modulate the activity of these proteins. Recently, it has become clear that the activity of several virulence‐related AraC family members is regulated through the direct interaction of protein ligands. These interactions, in general, function to activate or repress the transcription of virulence genes in response to specific extracellular stimuli. The identification and characterization of several protein ligands that modify the activity of AraC family members in Pseudomonas aeruginosa and Salmonella enterica are discussed herein.
Cryptococcus neoformans Kin1 protein kinase homologue, identified through a Caenorhabditis elegans screen, promotes virulence in mammals
Authors: Mylonakis Eleftherios , Idnurm Alexander , Moreno Roberto , El Khoury Joseph , Rottman James B. , Ausubel Frederick M. , Heitman Joseph , Calderwood Stephen B. 
Published: October 2004

SummaryCryptococcal infections are a global cause of significant morbidity and mortality. Recent studies support the hypothesis that virulence of Cryptococcus neoformans may have evolved via survival selection in environmental hosts, such as amoebae and free‐living nematodes. We used killing of the nematode Caenorhabditis elegans by C. neoformans as an assay to screen a library of random C. neoformans insertion mutants. Of 350 mutants tested, seven were identified with attenuated virulence that persisted after crossing the mutation back into a wild‐type strain. Genetic analysis of one strain revealed an insertion in a gene homologous to Saccharomyces cerevisiae KIN1, which encodes a serine/threonine protein kinase. C. neoformans kin1 mutants exhibited significant defects in virulence in murine inhalation and haematogenous infection models and displayed increased binding to alveolar and peritoneal macrophages. The kin1 mutant phenotypes were complemented by the wild‐type KIN1 gene. These findings show that the C. neoformans Kin1 kinase homologue is required for full virulence in disparate hosts and that C. elegans can be used as a substitute host to identify novel factors involved in fungal pathogenesis in mammals.
Functional diversity of photosynthesis during drought in a model tropical rainforest – the contributions of leaf area, photosynthetic electron transport and stomatal conductance to reduction in net ecosystem carbon exchange
Authors: RASCHER U. , BOBICH E. G. , LIN G. H. , WALTER A. , MORRIS T. , NAUMANN M. , NICHOL C. J. , PIERCE D. , BIL K. , KUDEYAROV V. , BERRY J. A. 
Published: October 2004

ABSTRACTThe tropical rainforest mesocosm within the Biosphere 2 Laboratory, a model system of some 110 species developed over 12 years under controlled environmental conditions, has been subjected to a series of comparable drought experiments during 2000–2002. In each study, the mesocosm was subjected to a 4–6 week drought, with well‐defined rainfall events before and after the treatment. Ecosystem CO2 uptake rate (Aeco) declined 32% in response to the drought, with changes occurring within days and being reversible within weeks, even though the deeper soil layers did not become significantly drier and leaf‐level water status of most large trees was not greatly affected. The reduced Aeco during the drought reflected both morphological and physiological responses. It is estimated that the drought‐induced 32% reduction of Aeco has three principal components: (1) leaf fall increased two‐fold whereas leaf expansion growth of some canopy dominants declined to 60%, leading to a 10% decrease in foliage coverage of the canopy. This might be the main reason for the persistent reduction of Aeco after rewatering. (2) The maximum photosynthetic electron transport rate at high light intensities in remaining leaves was reduced to 71% for three of the four species measured, even though no chronic photo‐inhibition occurred. (3) Stomata closed, leading to a reduced ecosystem water conductance to water vapour (33% of pre‐drought values), which not only reduced ecosystem carbon uptake rate, but may also have implications for water and energy budgets of tropical ecosystems. Additionally, individual rainforest trees responded differently, expressing different levels of stress and stress avoiding mechanisms. This functional diversity renders the individual response heterogeneous and has fundamental implications to scale leaf level responses to ecosystem dynamics.
Hydraulic architecture of leaf blades: where is the main resistance?
Authors: COCHARD H. , NARDINI A. , COLL L. 
Published: October 2004

ABSTRACTThe hydraulic architecture of Laurus nobilis L. and Juglans regia L. leaves was studied using three different approaches: (1) hydraulic measurements of both intact leaves and of leaves subjected to treatments aimed at removing the extra‐vascular resistance; (2) direct measurements of the vascular pressure with a pressure probe; and (3) modelling the hydraulic architecture of leaf venation system on the basis of measurements of vein densities and conductivities. The hydraulic resistance of leaves (Rleaf) either cut, boiled or frozen–thawed was reduced by about 60 and 85% with respect to control leaves for laurel and walnut, respectively. Direct pressure drop measurements suggested that 88% of the resistance resided outside the vascular system in walnut. Model simulations were in agreement with these results provided vein hydraulic conductance was 0.12–0.28 that of the conductance predicted by Poiseuille's law. The results suggest that Rleaf is dominated by substantial extra‐vascular resistances and therefore contrast with the conclusions of recent studies dealing with the hydraulic architecture of the leaf. The present study confirms the ‘classical’ view of the hydraulic architecture of leaves as composed by a low‐resistance component (the venation) and a high‐resistance component (the mesophyll).
The apparent feed‐forward response to vapour pressure deficit of stomata in droughted, field‐grown Eucalyptus globulus Labill
Authors: MACFARLANE C. , WHITE D. A. , ADAMS M. A. 
Published: October 2004

ABSTRACTThis study tested a multiplicative model of stomatal response to environment for drought‐affected trees of Eucalyptus globulus Labill. growing in southern Australia. The model incorporates a feed‐forward response to vapour pressure deficit of ambient air (δea) and performed well if evaluated using reduced major axis regression and log‐transformed   data.   There   was   strong   evidence   from gas‐exchange data, leaf water potentials and sapflow measurements of the feed‐forward response by stomata to leaf‐to‐air vapour pressure deficit (δel). The response of stomata to δel was irreversible. Stomatal conductance and the rate of net photosynthesis were highly correlated and declined, together with the rate of transpiration, throughout the afternoon as δea increased despite increasing leaf water potentials. The concentration of CO2 inside leaves (ci) increased as stomatal conductance declined indicating increasing non‐stomatal limitations to photosynthesis. The stomatal response to δel of E. globulus in the field is best described as an ‘apparent feed‐forward response’ that probably results from both slowly reversible depression of net photosynthesis and abscisic acid accumulation in guard cells. We suggest that the stomatal response to ci may strengthen the link between photosynthetic capacity and stomatal conductance during leaf drying as a result of either drought or large δ el.
Effect of potassium deficiency on the plasma membrane H+‐ATPase of the wood ray parenchyma in poplar
Authors: AREND M. , MONSHAUSEN G. , WIND C. , WEISENSEEL M. H. , FROMM J. 
Published: October 2004

ABSTRACTThe effect of K+ deficiency on the plasma membrane (PM) H+‐ATPase was studied in young stems of poplar plants (Populus tremula × tremuloides) grown with low or full‐strength K+ supply. Immunological assays using different antibodies were applied to test if K+ deficiency affects the amount of immunodetectable PM H+‐ATPases in the stem tissue. The monoclonal antibody clone 46 E5 B11 revealed an increased abundance of PM H+‐ATPases under conditions of low K+ supply, and immunolabelling experiments showed that this increase was restricted to vessel‐associated cells (VACs) of the wood ray parenchyma. Replacement of the monoclonal antibody by a polyclonal antibody against PM H+‐ATPase gave a specific immunoreactivity on blots as well as tissue sections too, but the labelling intensity showed no difference between plants with low or full‐strength K+ supply. Measurements of extracellular H+ concentrations using non‐invasive, H+‐selective microelectrodes revealed a lowering of the pH at the surface of VACs and an enhancement of net efflux of H+ in plants grown with low K+ supply. The present results indicate an up‐regulation of specific isoforms of the PM H+‐ATPase in VACs under K+‐deficient conditions and suggest a key role for these PM H+‐ATPases in unloading K+ from the xylem stream.
The plastidic nitrite transporter NAR1;1 improves nitrate use efficiency for growth in Chlamydomonas
Authors: MARISCAL V. , REXACH J. , FERNÁNDEZ E. , GALVÁN A. 
Published: October 2004

ABSTRACTThe Chlamydomonas reinhardtii Nar1;1 gene encodes a membrane protein involved in nitrite transport to the chloroplast and is apparently dispensable for nitrate/nitrite‐dependent growth in some conditions (Rexach, Fernández & Galván, Plant Cell 12, 1441–1454, 2000). In the present study the question of when NAR1;1 is required and how it improves nitrate utilization for growth was investigated. Comparative studies were performed with strains Nar1;1+ and Nar1;1– in nitrate media under three experimental conditions. Under continuous light and high CO2 (5%), strains containing or lacking Nar1;1 showed a very similar nitrate‐dependent growth. Under continuous light and low CO2 (air), Nar1;1 allowed a slightly higher growth in nitrate. However, under light/dark cycles and low CO2, the strain having Nar1;1 showed a higher nitrate‐dependent growth and doubled the amount of protein and chlorophyll than the Nar1;1– strain. The activities for nitrate uptake, nitrite and ammonium excretions, nitrate and nitrite reductases, glutamine synthetase (GS), as well as the transcript levels of Nar1;1, Nrt2;1, Nar2, Nrt2;3 and GS1 and GS2 genes were determined under this third condition by trying to understand how NAR1;1 improves nitrate use efficiency. Nitrite and ammonium excretion, which was higher in the strain Nar1;1– than in Nar1;1+, results in an important deregulation in the gene expression of nitrate transporters and cytosolic GS1. These data lead to the proposal that nitrite transport to the chloroplast mediated by NAR1;1 allows a balanced expression of enzymes and transporters for nitrate assimilation, thus optimizing nitrate utilization under the natural condition of light/dark cycles and air.
Oxidant and antioxidant levels in preterm newborns with idiopathic hyperbilirubinaemia
Authors: Turgut M , Başaran O , Çekmen M , Karataş F , Kurt A , Aygün AD 
Published: October 2004

Objectives:  Newborns, particulary preterm infants, have limited antioxidant protective capacity. The organism's defence system against reactive oxygen species including vitamins A, E and C, trace element selenium (Se) and enzymes, such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH‐Px) are essential components of the antioxidant system against the oxidative injury to the cellular membranes of erythrocytes. In this study, our aim was to compare the oxidant nitric oxide (total plasma nitrite level as an indicator of nitric oxide (NO)), antioxidant vitamins and selenium and erythrocyte antioxidant enzymes in premature babies with hyperbilirubinaemia with healthy preterms.Methods:  Twenty preterm infants with newborn jaundice were included in the study group, while 15 preterm infants without jaundice were enrolled in the control group. We evaluated the mean plasma levels of, respectively, the total nitrite as an indicator of NO, bilirubin, vitamins A, E, C and selenium, and the activity of erythrocyte antioxidant enzymes such as CAT, SOD and GSH‐Px of preterm infants with idiopathic hyperbilirubinaemia and compared to those of the control group.Results:  The mean plasma total nitrite and total serum bilirubin levels and blood reticulocyte counts of the study group were found to be significantly higher than those of the control group (P < 0.001, P < 0.001 and P < 0.05, respectively). Furthermore, the activity of erythrocyte antioxidant enzymes (all P < 0.001) and the mean plasma levels of the antioxidant vitamins A, E, and C (P < 0.05, P < 0.05 and P < 0.001, respectively) and selenium (P < 0.001) of the study group were all found to be significantly lower than those of the control group.Conclusion:  We hypothesize that low antioxidants in pretem babies may predispose them to increased oxidative stress, and cause hyperbilirubinaemia.
Schizosaccharomyces pombe
Pmr1p Is Essential for Cell Wall Integrity and Is Required for Polarized Cell Growth and Cytokinesis
Authors: Cortés Juan Carlos G. , Katoh-Fukui Reiko , Moto Kanako , Ribas Juan Carlos , Ishiguro Junpei 
Published: October 2004

ABSTRACT

The
cps5
-
138
fission yeast mutant shows an abnormal lemon-like morphology at 28°C in minimal medium and a lethal thermosensitive phenotype at 37°C. Cell growth is completely inhibited at 28°C in a Ca
2+
-free medium, in which the wild type is capable of growing normally. Under these conditions, actin patches become randomly distributed throughout the cell, and defects in septum formation and subsequent cytokinesis appear. The mutant cell is hypersensitive to the cell wall-digesting enzymatic complex Novozym234 even under permissive conditions. The gene SPBC31E1.02c, which complements all the mutant phenotypes described above, was cloned and codes for the Ca
2+
-ATPase homologue Pmr1p. The gene is not essential under optimal growth conditions but is required under conditions of low Ca
2+
(<0.1 mM) or high temperature (>35°C). The green fluorescent protein-tagged Cps5 proteins, which are expressed under physiological conditions (an integrated single copy with its own promoter in the
cps5
Δ strain), display a localization pattern typical of endoplasmic reticulum proteins. Biochemical analyses show that 1,3-β-
d
-glucan synthase activity in the mutant is decreased to nearly half that of the wild type and that the mutant cell wall contains no detectable galactomannan when the cells are exposed to a Ca
2+
-free medium. The mutant acid phosphatase has an increased electrophoretic mobility, suggesting that incomplete protein glycosylation takes place in the mutant cells. These results indicate that
S. pombe
Pmr1p is essential for the maintenance of cell wall integrity and cytokinesis, possibly by allowing protein glycosylation and the polarized actin distribution to take place normally. Disruption and complementation analyses suggest that Pmr1p shares its function with a vacuolar Ca
2+
-ATPase homologue, Pmc1p (SPAPB2B4.04c), to prevent lethal activation of calcineurin for cell growth.
Epigenetic Control of Chromosome Breakage at the 5′ End of
Paramecium tetraurelia
Gene
A
Authors: Amar Laurence , Dubrana Karine 
Published: October 2004

ABSTRACT

Macronuclei and micronuclei of ciliates have related genomes, with macronuclei developing from zygotic micronuclei through programmed DNA rearrangements. While
Paramecium tetraurelia
wild-type strain 51 and mutant strain d48 have the same micronuclear genome, qualitative differences between their macronuclear genomes have been described, demonstrating that programmed DNA rearrangements could be epigenetically controlled in ciliates. Macronuclear chromosomes end downstream of gene
A
(A51 Mac ends) and at the 5′ end of gene
A
(Ad48 Mac ends) in strains 51 and d48, respectively. To gain further insight into the process of chromosome end formation, we performed an extensive analysis of locus
A
rearrangement in strains d48 and 51, in strain d12, which harbors a gene
A
deletion, and in interstrain cross progeny. We show that (i) allele

A
d12

harbors a deletion of >16 kb, (ii) A51 Mac ends distribute over four rather than three DNA regions, (iii) strains d48 and 51 display only quantitative differences (rare Ad48 and A51 Mac ends do form in strains 51 and d48, respectively), (iv) the level of A51 Mac ends is severalfold enhanced in d12- and d48-derived progeny, and (v) this level inversely correlates with the level of Ad48 Mac ends in the d48 parent. Together, these data lead to a model in which the formation of Ad48 Mac ends is epigenetically controlled by a d48 factor(s). We propose that the d48 factor(s) may be derived from RNA molecules transcribed from the Ad48 Mac ends and encompassing the truncated
A
gene and telomeric repeats.
Pmt-Mediated O Mannosylation Stabilizes an Essential Component of the Secretory Apparatus, Sec20p, in
Candida albicans
Authors: Weber Yvonne , Prill Stephan K.-H. , Ernst Joachim F. 
Published: October 2004

ABSTRACT

Sec20p is an essential endoplasmic reticulum (ER) membrane protein in yeasts, functioning as a tSNARE component in retrograde vesicle traffic. We show that Sec20p in the human fungal pathogen
Candida albicans
is extensively O mannosylated by protein mannosyltransferases (Pmt proteins). Surprisingly, Sec20p occurs at wild-type levels in a
pmt6
mutant but at very low levels in
pmt1
and
pmt4
mutants and also after replacement of specific Ser/Thr residues in the lumenal domain of Sec20p. Pulse-chase experiments revealed rapid degradation of unmodified Sec20p (38.6 kDa) following its biosynthesis, while the stable O
-
glycosylated form (50 kDa) was not formed in a
pmt1
mutant. These results suggest a novel function of O mannosylation in eukaryotes, in that modification by specific Pmt proteins will prevent degradation of ER-resident membrane proteins via ER-associated degradation or a proteasome-independent pathway.
Presence of a Poly(A) Binding Protein and Two Proteins with Cell Cycle-Dependent Phosphorylation in
Crithidia fasciculata
mRNA Cycling Sequence Binding Protein II
Authors: Mittra Bidyottam , Ray Dan S. 
Published: October 2004

ABSTRACT

Crithidia fasciculata
cycling sequence binding proteins (CSBP) have been shown to bind with high specificity to sequence elements present in several mRNAs that accumulate periodically during the cell cycle. The first described CSBP has subunits of 35.6 (CSBPA) and 42 kDa (CSBPB). A second distinct binding protein termed CSBP II has been purified from
CSBPA
null mutant cells, lacking both CSBPA and CSBPB proteins, and contains three major polypeptides with predicted molecular masses of 63, 44.5, and 33 kDa. Polypeptides of identical size were radiolabeled in UV cross-linking assays performed with purified CSBP II and
32
P-labeled RNA probes containing six copies of the cycling sequence. The CSBP II binding activity was found to cycle in parallel with target mRNA levels during progression through the cell cycle. We have cloned genes encoding these three CSBP II proteins, termed RBP63, RBP45, and RBP33, and characterized their binding properties. The RBP63 protein is a member of the poly(A) binding protein family. Homologs of RBP45 and RBP33 proteins were found only among the kinetoplastids. Both RBP45 and RBP33 proteins and their homologs have a conserved carboxy-terminal half that contains a PSP1-like domain. All three CSBP II proteins show specificity for binding the wild-type cycling sequence in vitro. RBP45 and RBP33 are phosphoproteins, and RBP45 has been found to bind in vivo specifically to target mRNA containing cycling sequences. The levels of phosphorylation of both RBP45 and RBP33 were found to cycle during the cell cycle.