bluuebunny/crossref_metadata_2025_split huggingface dataset:
In the Yeast Heat Shock Response, Hsf1-Directed Induction of Hsp90 Facilitates the Activation of the Slt2 (Mpk1) Mitogen-Activated Protein Kinase Required for Cell Integrity
Authors: Truman Andrew W. , Millson Stefan H. , Nuttall James M. , Mollapour Mehdi , Prodromou Chrisostomos , Piper Peter W. 
Published: February 2007

ABSTRACT

Yeast is rendered temperature sensitive with loss of the C-terminal (CT) domain of heat shock transcription factor (Hsf1). This domain loss was found to abrogate heat stimulation of Slt2 (Mpk1), the mitogen-activated protein kinase that directs the reinforced cell integrity gene expression needed for high-temperature growth. In Hsf1 CT domain-deficient cells, Slt2 still undergoes Mkk1/2-directed dual-Thr/Tyr phosphorylation in response to the heat stimulation of cell integrity pathway signaling, but the low Hsp90 expression level suppresses any corresponding increase in Slt2 kinase activity due to Slt2 being a “client” of the Hsp90 chaperone. A non-Hsf1-directed Hsp90 overexpression restored the heat induction of Slt2 activity in these cells, as well as both Slt2-dependent (Rlm1, Swi4) and Slt2-independent (MBF) transcriptional activities. Their high-temperature growth was also rescued, not just by this Hsp90 overexpression but by osmotic stabilization, by the expression of a Slt2-independent form of the Rlm1 transcriptional regulator of cell integrity genes, and by a multicopy
SLT2
gene vector. In providing the elevated Hsp90 needed for an efficient activation of Slt2, heat activation of Hsf1 indirectly facilitates (Slt2-directed) heat activation of yet another transcription factor (Rlm1). This provides an explanation as to why, in earlier transcript analysis compared to chromatin immunoprecipitation studies, many more genes of yeast displayed an Hsf1-dependent transcriptional activation by heat than bound Hsf1 directly. The levels of Hsp90 expression affecting transcription factor regulation by Hsp90 client protein kinases also provides a mechanistic model for how heat shock factor can influence the expression of several non-
hsp
genes in higher organisms.
Molecular and Biochemical Characterization of a Novel Intracellular Invertase fromAspergillus nigerwith Transfructosylating Activity
Authors: Goosen Coenie , Yuan Xiao-Lian , van Munster Jolanda M. , Ram Arthur F. J. , van der Maarel Marc J. E. C. , Dijkhuizen Lubbert 
Published: February 2007

ABSTRACTA novel subfamily of putative intracellular invertase enzymes (glycoside hydrolase family 32) has previously been identified in fungal genomes. Here, we report phylogenetic, molecular, and biochemical characteristics of SucB, one of two novel intracellular invertases identified inAspergillus niger. ThesucBgene was expressed inEscherichia coliand an invertase-negative strain ofSaccharomyces cerevisiae. Enzyme purified fromE. colilysate displayed a molecular mass of 75 kDa, judging from sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Its optimum pH and temperature for sucrose hydrolysis were determined to be 5.0 and 37 to 40°C, respectively. In addition to sucrose, the enzyme hydrolyzed 1-kestose, nystose, and raffinose but not inulin and levan. SucB produced 1-kestose and nystose from sucrose and 1-kestose, respectively. With nystose as a substrate, products up to a degree of polymerization of 4 were observed. SucB displayed typical Michaelis-Menten kinetics with substrate inhibition on sucrose (apparentKm,Ki, andVmaxof 2.0 ± 0.2 mM, 268.1 ± 18.1 mM, and 6.6 ± 0.2 μmol min−1mg−1of protein [total activity], respectively). At sucrose concentrations up to 400 mM, transfructosylation (FTF) activity contributed approximately 20 to 30% to total activity. At higher sucrose concentrations, FTF activity increased to up to 50% of total activity. Disruption ofsucBinA. nigerresulted in an earlier onset of sporulation on solid medium containing various carbon sources, whereas no alteration of growth in liquid culture medium was observed. SucB thus does not play an essential role in inulin or sucrose catabolism inA. nigerbut may be needed for the intracellular conversion of sucrose to fructose, glucose, and small oligosaccharides.
Retinal Biosynthesis in Fungi: Characterization of the Carotenoid Oxygenase CarX fromFusarium fujikuroi
Authors: Prado-Cabrero Alfonso , Scherzinger Daniel , Avalos Javier , Al-Babili Salim 
Published: February 2007

ABSTRACTThecargene cluster of the ascomyceteFusarium fujikuroiencodes two enzymes responsible for torulene biosynthesis (CarRA and CarB), an opsin-like protein (CarO), and a putative carotenoid cleaving enzyme (CarX). It was presumed that CarX catalyzes the formation of the major carotenoid inF. fujikuroi, neurosporaxanthin, a cleavage product of torulene. However, targeted deletion ofcarXdid not impede neurosporaxanthin biosynthesis. On the contrary, ΔcarXmutants showed a significant increase in the total carotenoid content, indicating an involvement of CarX in the regulation of the pathway. In this work, we investigated the enzymatic activity of CarX. The expression of the enzyme in β-carotene-accumulatingEscherichia colicells led to the formation of the opsin chromophore retinal. The identity of the product was proven by high-performance liquid chromatography and gas chromatography-mass spectrometry. Subsequent in vitro assays with heterologously expressed and purified CarX confirmed its β-carotene-cleaving activity and revealed its capability to produce retinal also from other substrates, such as γ-carotene, torulene, and β-apo-8′-carotenal. Our data indicate that the occurrence of at least one β-ionone ring in the substrate is required for the cleavage reaction and that the cleavage site is determined by the distance to the β-ionone ring. CarX represents the first retinal-synthesizing enzyme reported in the fungal kingdom so far. It seems likely that the formed retinal is involved in the regulation of the carotenoid biosynthetic pathway via a negative feedback mechanism.
Role of DNA Repair by Nonhomologous-End Joining in
Bacillus subtilis
Spore Resistance to Extreme Dryness, Mono- and Polychromatic UV, and Ionizing Radiation
Authors: Moeller Ralf , Stackebrandt Erko , Reitz Günther , Berger Thomas , Rettberg Petra , Doherty Aidan J. , Horneck Gerda , Nicholson Wayne L. 
Published: February 2007

ABSTRACT

The role of DNA repair by nonhomologous-end joining (NHEJ) in spore resistance to UV, ionizing radiation, and ultrahigh vacuum was studied in wild-type and DNA repair mutants (
recA
,
splB
,
ykoU
,
ykoV
, and
ykoU ykoV
mutants) of
Bacillus subtilis
. NHEJ-defective spores with mutations in
ykoU
,
ykoV
, and
ykoU ykoV
were significantly more sensitive to UV, ionizing radiation, and ultrahigh vacuum than wild-type spores, indicating that NHEJ provides an important pathway during spore germination for repair of DNA double-strand breaks.
Catalytic Properties of
Staphylococcus aureus
and
Bacillus
Members of the Secondary Cation/Proton Antiporter-3 (Mrp) Family Are Revealed by an Optimized Assay in an
Escherichia coli
Host
Authors: Swartz Talia H. , Ito Masahiro , Ohira Takayuki , Natsui Shinsuke , Hicks David B. , Krulwich Terry A. 
Published: February 2007

ABSTRACT

Monovalent cation proton antiporter-3 (Mrp) family antiporters are widely distributed and physiologically important in prokaryotes. Unlike other antiporters, they require six or seven hydrophobic gene products for full activity. Standard fluorescence-based assays of Mrp antiport in membrane vesicles from
Escherichia coli
transformants have not yielded strong enough signals for characterization of antiport kinetics. Here, an optimized assay protocol for vesicles of antiporter-deficient
E. coli
EP432 transformants produced higher levels of secondary Na
+
(Li
+
)/H
+
antiport than previously reported. Assays were conducted on Mrps from alkaliphilic
Bacillus pseudofirmus
OF4 and
Bacillus subtilis
and the homologous antiporter of
Staphylococcus aureus
(Mnh), all of which exhibited Na
+
(Li
+
)/H
+
antiport. A second paralogue of
S. aureus
(Mnh2) did not. K
+
, Ca
2+
, and Mg
2+
did not support significant antiport by any of the test antiporters. All three Na
+
(Li
+
)/H
+
Mrp antiporters had alkaline pH optima and apparent

K
m

values for Na
+
that are among the lowest reported for bacterial Na
+
/H
+
antiporters. Using a fluorescent probe of the transmembrane electrical potential (ΔΨ), Mrp Na
+
/H
+
antiport was shown to be ΔΨ consuming, from which it is inferred to be electrogenic. These assays also showed that membranes from
E. coli
EP432 expressing Mrp antiporters generated higher ΔΨ levels than control membranes, as did membranes from
E. coli
EP432 expressing plasmid-borne NhaA, the well-characterized electrogenic
E. coli
antiporter. Assays of respiratory chain components in membranes from Mrp and control
E. coli
transformants led to a hypothesis explaining how activity of secondary, ΔΨ-consuming antiporters can elicit increased capacity for ΔΨ generation in a bacterial host.
Isolation of the
rstA
Gene as a Multicopy Suppressor of YjeE, an Essential ATPase of Unknown Function in
Escherichia coli
Authors: Campbell Tracey L. , Ederer Claudia S. , Allali-Hassani Abdellah , Brown Eric D. 
Published: February 2007

ABSTRACT

YjeE is an essential ATPase in
Escherichia coli
whose cellular function remains uncharacterized. Using a genomic library, we have identified
rstA
as a multicopy suppressor of a conditional
yjeE
deletion strain. High-copy
rstA
is the first recorded suppressor for a lesion in
yjeE
, and this newly charted genetic interaction has the potential to be informative about the function, with further study of the interacting partners.
The Genome Sequence of Avian PathogenicEscherichia coliStrain O1:K1:H7 Shares Strong Similarities with Human Extraintestinal PathogenicE. coliGenomes
Authors: Johnson Timothy J. , Kariyawasam Subhashinie , Wannemuehler Yvonne , Mangiamele Paul , Johnson Sara J. , Doetkott Curt , Skyberg Jerod A. , Lynne Aaron M. , Johnson James R. , Nolan Lisa K. 
Published: February 2007

ABSTRACTEscherichia colistrains that cause disease outside the intestine are known as extraintestinal pathogenicE. coli(ExPEC) and include human uropathogenicE. coli(UPEC) and avian pathogenicE. coli(APEC). Regardless of host of origin, ExPEC strains share many traits. It has been suggested that these commonalities may enable APEC to cause disease in humans. Here, we begin to test the hypothesis that certain APEC strains possess potential to cause human urinary tract infection through virulence genotyping of 1,000 APEC and UPEC strains, generation of the first complete genomic sequence of an APEC (APEC O1:K1:H7) strain, and comparison of this genome to all available human ExPEC genomic sequences. The genomes of APEC O1 and three human UPEC strains were found to be remarkably similar, with only 4.5% of APEC O1's genome not found in other sequenced ExPEC genomes. Also, use of multilocus sequence typing showed that some of the sequenced human ExPEC strains were more like APEC O1 than other human ExPEC strains. This work provides evidence that at least some human and avian ExPEC strains are highly similar to one another, and it supports the possibility that a food-borne link between some APEC and UPEC strains exists. Future studies are necessary to assess the ability of APEC to overcome the hurdles necessary for such a food-borne transmission, and epidemiological studies are required to confirm that such a phenomenon actually occurs.
Influence of Amino Acids on Low-Density
Escherichia coli
Responses to Nutrient Downshifts
Authors: Bodini Sergio , Nunziangeli Luisa , Santori Francesca 
Published: February 2007

ABSTRACT

A vast bibliography on nutrient effects on high-density cultures exists, while it has been overlooked that low densities of starving cells are often the rule in natural environments. By means of a novel sensitive β-galactosidase assay, we examined
Escherichia coli
transitions to minimal media when the cell concentration was 100 to 10,000 cells per ml. As in high-density cultures, the enzyme activity depended on amino acid availability and was subject to catabolite repression and stringent control. In all conditions tested, despite the presence of other nutrient sources, the relationship between β-galactosidase activity and the
l
-amino acid pool was hyperbolic. The affinity constant when the amino acid pool was the only nutrient source averaged 14 μM after 90 min and increased up to 222 μM after 4.5 h. While investigating the transition from lag phase to exponential phase, we observed that the cells did not enter into starvation mode in the presence of amino acids, even when the nutrient amount was insufficient to support full survival. Based on these premises, the switch from starvation to hunger was investigated in relation to the amino acid pools. A critical range of concentrations at which
E. coli
linearly synthesized β-galactosidase despite, at the same time, suffering a large decrease in cell viability was then recognized. Since both β-galactosidase production and the dilution rate were reduced by more than half in the absence of leucine, we examined the contribution of leucine to cell recovery capabilities.
Mechanisms of Adaptation to Nitrosative Stress inBacillus subtilis
Authors: Rogstam Annika , Larsson Jonas T. , Kjelgaard Peter , von Wachenfeldt Claes 
Published: February 2007

ABSTRACTBacteria use a number of mechanisms for coping with the toxic effects exerted by nitric oxide (NO) and its derivatives. Here we show that the flavohemoglobin encoded by thehmpgene has a vital role in an adaptive response to protect the soil bacteriumBacillus subtilisfrom nitrosative stress. We further show that nitrosative stress induced by the nitrosonium cation donor sodium nitroprusside (SNP) leads to deactivation of the transcriptional repressor NsrR, resulting in derepression ofhmp. Nitrosative stress induces the sigma B-controlled general stress regulon. However, asigBnull mutant did not show increased sensitivity to SNP, suggesting that the sigma B-dependent stress proteins are involved in a nonspecific protection against stress whereas the Hmp flavohemoglobin plays a central role in detoxification. Mutations in theyjbIHoperon, which encodes a truncated hemoglobin (YjbI) and a predicted 34-kDa cytosolic protein of unknown function (YjbH), renderedB. subtilishypersensitive to SNP, suggesting roles in nitrosative stress management.
A
pthA
Homolog from
Xanthomonas axonopodis
pv. citri Responsible for Host-Specific Suppression of Virulence
Authors: Shiotani Hiroshi , Fujikawa Takashi , Ishihara Hiromichi , Tsuyumu Sinji , Ozaki Katsumi 
Published: February 2007

ABSTRACT

Strains of the plant-pathogenic bacterium
Xanthomonas axonopodis
pv. citri are differentiated into two groups with respect to aggressiveness (normal and weak) on
Citrus grandis
cultivars but not on other
Citrus
species such as
Citrus sinensis
. Random mutagenesis using the transposon Tn
5
in
X. axonopodis
pv. citri strain KC21, which showed weak aggressiveness on a
C. grandis
cultivar, was used to isolate mutant KC21T46, which regained a normal level of aggressiveness on the cultivar. The gene inactivated by the transposon,
hssB3.0
, was shown to be responsible for the suppression of virulence on
C. grandis
. Sequence analysis revealed it to be a new member of the
pthA
homologs, which was almost identical in sequence to the other homologs except for the number of tandem repeats in the central region of the gene.
hssB3.0
appears to be a chimera of other
pthA
homologs,
pB3.1
and
pB3.7
, and could have been generated by recombination between these two genes. Importantly, in
X. axonopodis
pv. citri,
hssB3.0
was found in all of the tested isolates belonging to the weakly aggressive group but not in the isolates of the normally aggressive group. Isolation of the virulence-deficient mutant KC21T14 from KC21, in which the pathogenicity gene
pthA-KC21
was disrupted, showed that
hssB3.0
induces a defense response on the host but partially interrupts canker development elicited by the pathogenicity gene in this bacterium.
YcfR (BhsA) InfluencesEscherichia coliBiofilm Formation through Stress Response and Surface Hydrophobicity
Authors: Zhang Xue-Song , García-Contreras Rodolfo , Wood Thomas K. 
Published: February 2007

ABSTRACTDNA microarrays revealed that expression ofycfR, which encodes a putative outer membrane protein, is significantly induced inEscherichia colibiofilms and is also induced by several stress conditions. We show that deletion ofycfRincreased biofilm formation fivefold in the presence of glucose; the glucose effect was corroborated by showing binding of the cyclic AMP receptor protein to theycfRpromoter. It appears that YcfR is a multiple stress resistance protein, since deletingycfRalso rendered the cell more sensitive to acid, heat treatment, hydrogen peroxide, and cadmium. Increased biofilm formation through YcfR due to stress appears to be the result of decreasing indole synthesis, since a mutation in thetnaAgene encoding tryptophanase prevented enhanced biofilm formation upon stress and adding indole prevented enhanced biofilm formation upon stress. DeletingycfRalso affected outer membrane proteins and converted the cell from hydrophilic to hydrophobic, as well as increased cell aggregation fourfold. YcfR seems to be involved in the regulation ofE. coliK-12 biofilm formation by decreasing cell aggregation and cell surface adhesion, by influencing the concentration of signal molecules, and by interfering with stress responses. Based on our findings, we propose that this locus be namedbhsA, for influencingbiofilm throughhydrophobicity andstress response.
Ribosomal Features Essential for
tna
Operon Induction: Tryptophan Binding at the Peptidyl Transferase Center
Authors: Cruz-Vera Luis R. , New Aaron , Squires Catherine , Yanofsky Charles 
Published: February 2007

ABSTRACT

Features of the amino acid sequence of the TnaC nascent peptide are recognized by the translating ribosome. Recognition leads to tryptophan binding within the translating ribosome, inhibiting the termination of
tnaC
translation and preventing Rho-dependent transcription termination in the
tna
operon leader region. It was previously shown that inserting an adenine residue at position 751 or introducing the U2609C change in 23S rRNA or introducing the K90W replacement in ribosomal protein L22 prevented tryptophan induction of
tna
operon expression. It was also observed that an adenine at position 752 of 23S rRNA was required for induction. In the current study, the explanation for the lack of induction by these altered ribosomes was investigated. Using isolated TnaC-ribosome complexes, it was shown that although tryptophan inhibits puromycin cleavage of TnaC-tRNA
Pro
with wild-type ribosome complexes, it does not inhibit cleavage with the four mutant ribosome complexes examined. Similarly, tryptophan prevents sparsomycin inhibition of TnaC-tRNA
Pro
cleavage with wild-type ribosome complexes but not with these mutant ribosome complexes. Additionally, a nucleotide located close to the peptidyl transferase center, A2572, which was protected from methylation by tryptophan with wild-type ribosome complexes, was not protected with mutant ribosome complexes. These findings identify specific ribosomal residues located in the ribosome exit tunnel that recognize features of the TnaC peptide. This recognition creates a free tryptophan-binding site in the peptidyl transferase center, where bound tryptophan inhibits peptidyl transferase activity.
Physiological Effects of Crl in
Salmonella
Are Modulated by σ
S
Level and Promoter Specificity
Authors: Robbe-Saule Véronique , Lopes Miguel Dias , Kolb Annie , Norel Françoise 
Published: February 2007

ABSTRACT

The small regulatory protein Crl activates σ
S
(RpoS), the stationary-phase and general stress response sigma factor. Crl has been reported to bind σ
S
in vitro and to facilitate the formation of RNA polymerase holoenzyme. In
Salmonella enterica
serovar Typhimurium, Crl is required for the development of the rdar morphotype and transcription initiation of the σ
S
-dependent genes
csgD
and
adrA
, involved in curli and cellulose production. Here, we examined the expression of other σ
S
-dependent phenotypes and genes in a Δ
crl
mutant of
Salmonella
. Gene fusion analyses and in vitro transcription assays indicate that the magnitude of Crl activation differs between promoters and is highly dependent on σ
S
levels. We replaced the wild-type
rpoS
allele in
S. enterica
serovar Typhimurium strain ATCC 14028 with the
rpoS
LT2
allele that shows reduced expression of σ
S
; the result was an increased Crl activation ratio and larger physiological effects of Crl on oxidative, thermal, and acid stress resistance levels during stationary phase. We also found that
crl
,
rpoS
, and
crl rpoS
strains grew better on succinate than did the wild type and expressed the succinate dehydrogenase
sdhCDBA
operon more strongly. The
crl
and
rpoS
LT2
mutations also increased the competitive fitness of
Salmonella
in stationary phase. These results show that Crl contributes to negative regulation by σ
S
, a finding consistent with a role for Crl in sigma factor competition via the facilitation of σ
S
binding to core RNA polymerase.
In Vitro Analysis of the Two-Component System MtrB-MtrA from
Corynebacterium glutamicum
Authors: Möker Nina , Krämer Jens , Unden Gottfried , Krämer Reinhard , Morbach Susanne 
Published: February 2007

ABSTRACT

The two-component system MtrBA is involved in the osmostress response of
Corynebacterium glutamicum
. MtrB was reconstituted in a functionally active form in liposomes and showed autophosphorylation and phosphatase activity. In proteoliposomes, MtrB activity was stimulated by monovalent cations used by many osmosensors for the detection of hypertonicity. Although MtrB was activated by monovalent cations, they lead in vitro to a general stabilization of histidine kinases and do not represent the stimulus for MtrB to sense hyperosmotic stress.
Psychological determinants of risk taking by children: an integrative model and implications for interventions: Figure 1
Authors: Morrongiello Barbara A , Lasenby-Lessard Jennifer 
Published: February 2007

Objectives:To draw on empirical findings of the psychological factors that cause elementary-school children to engage in risky play behaviors that can lead to injury, with the aim of developing an integrative model that can support intervention-program planning.Methods:An extensive review of literature on this topic was conducted, determinants of risk taking for which there was empirical support were identified, and results were synthesized to create an integrative model of children’s risk taking.Results:Research on risk taking in children is limited, but the findings support the importance of examining child, family and socio-environmental factors to understand children’s risk-taking behaviors.Conclusions:Development of a model outlining the determinants of risk behaviors can provide a foundation for initiatives that aim to reduce such behaviors and prevent childhood injuries.