bluuebunny/crossref_metadata_2025_split huggingface dataset:
Candida albicans
Tup1 Is Involved in Farnesol-Mediated Inhibition of Filamentous-Growth Induction
Authors: Kebaara Bessie W. , Langford Melanie L. , Navarathna Dhammika H. M. L. P. , Dumitru Raluca , Nickerson Kenneth W. , Atkin Audrey L. 
Published: April 2008

ABSTRACT

Candida albicans
is a dimorphic fungus that can interconvert between yeast and filamentous forms. Its ability to regulate morphogenesis is strongly correlated with virulence. Tup1, a transcriptional repressor, and the signaling molecule farnesol are both capable of negatively regulating the yeast to filamentous conversion. Based on this overlap in function, we tested the hypothesis that the cellular response to farnesol involves, in part, the activation of Tup1. Tup1 functions with the DNA binding proteins Nrg1 and Rfg1 as a transcription regulator to repress the expression of hypha-specific genes. The
tup1/tup1
and
nrg1/nrg1
mutants, but not the
rfg1/rfg1
mutant, failed to respond to farnesol. Treatment of
C. albicans
cells with farnesol caused a small but consistent increase in both
TUP1
mRNA and protein levels. Importantly, this increase corresponds with the commitment point, beyond which added farnesol no longer blocks germ tube formation, and it correlates with a strong decrease in the expression of two Tup1-regulated hypha-specific genes,
HWP1
and
RBT1
. Tup1 probably plays a direct role in the response to farnesol because farnesol suppresses the haploinsufficient phenotype of a
TUP1/tup1
heterozygote. Farnesol did not affect
EFG1
(a transcription regulator of filament development),
NRG1
, or
RFG1
mRNA levels, demonstrating specific gene regulation in response to farnesol. Furthermore, the
tup1/tup1
and
nrg1/nrg1
mutants produced 17- and 19-fold more farnesol, respectively, than the parental strain. These levels of excess farnesol are sufficient to block filamentation in a wild-type strain. Our data are consistent with the role of Tup1 as a crucial component of the response to farnesol in
C. albicans
.
Transcriptional Interference and Repression Modulate the Conjugative Ability of the Symbiotic Plasmid of
Rhizobium etli
Authors: Sepúlveda Edgardo , Pérez-Mendoza Daniel , Ramírez-Romero Miguel A. , Soto María J. , López-Lara Isabel M. , Geiger Otto , Sanjuán Juan , Brom Susana , Romero David 
Published: April 2008

ABSTRACT

Bacteria of the order
Rhizobiales
are able to establish nitrogen-fixing symbioses with legumes. Commonly, genes for symbiosis are harbored on large symbiotic plasmids. Although the transfer of symbiotic plasmids is commonly detected in nature, there are few experimentally characterized examples. In
Rhizobium etli
, the product of
rctA
inhibits the conjugation of the symbiotic plasmid by reducing the transcription of the
virB
operon.
rctA
is transcribed divergently from this operon, and its product is predicted to have a DNA binding domain. In the present study, using DNase I footprinting and binding assays, we demonstrated the specific binding of RctA to the
virB
operon promoter. A 9-bp motif in the spacer region of this promoter (the
rctA
binding motif box) and the presence of a functional −10 region were critical elements for RctA binding. Transcriptional fusion analyses revealed that the elimination of either element provoked a relief of RctA-mediated repression. These data support a model in which RctA inhibits the access of the RNA polymerase to the
virB
promoter. Interestingly,
rctA
expression levels were modulated by transcriptional interference from transcripts emanating from the
virB
promoter. This phenomenon adds another level of regulation for this system, thus revealing a novel mechanism of plasmid transfer regulation in the
Rhizobiales
.
Bacteriophage P22 Antitermination boxB Sequence Requirements Are Complex and Overlap with Those of λ
Authors: Cocozaki Alexis I. , Ghattas Ingrid R. , Smith Colin A. 
Published: April 2008

ABSTRACT

Transcription antitermination in phages λ and P22 uses N proteins that bind to similar boxB RNA hairpins in regulated transcripts. In contrast to the λ N-boxB interaction, the P22 N-boxB interaction has not been extensively studied. A nuclear magnetic resonance structure of the P22 N peptide boxB
left
complex and limited mutagenesis have been reported but do not reveal a consensus sequence for boxB. We have used a plasmid-based antitermination system to screen boxBs with random loops and to test boxB mutants. We find that P22 N requires boxB to have a GNRA-like loop with no simple requirements on the remaining sequences in the loop or stem. U:A or A:U base pairs are strongly preferred adjacent to the loop and appear to modulate N binding in cooperation with the loop and distal stem. A few GNRA-like hexaloops have moderate activity. Some boxB mutants bind P22 and λ N, indicating that the requirements imposed on boxB by P22 N overlap those imposed by λ N. Point mutations can dramatically alter boxB specificity between P22 and λ N. A boxB specific for P22 N can be mutated to λ N specificity by a series of single mutations via a bifunctional intermediate, as predicted by neutral theories of evolution.
UpaG, a New Member of the Trimeric Autotransporter Family of Adhesins in UropathogenicEscherichia coli
Authors: Valle Jaione , Mabbett Amanda N. , Ulett Glen C. , Toledo-Arana Alejandro , Wecker Karine , Totsika Makrina , Schembri Mark A. , Ghigo Jean-Marc , Beloin Christophe 
Published: April 2008

ABSTRACTThe ability ofEscherichia colito colonize both intestinal and extraintestinal sites is driven by the presence of specific virulence factors, among which are the autotransporter (AT) proteins. Members of the trimeric AT adhesin family are important virulence factors for several gram-negative pathogens and mediate adherence to eukaryotic cells and extracellular matrix (ECM) proteins. In this study, we characterized a new trimeric AT adhesin (UpaG) from uropathogenicE. coli(UPEC). Molecular analysis of UpaG revealed that it is translocated to the cell surface and adopts a multimeric conformation. We demonstrated that UpaG is able to promote cell aggregation and biofilm formation on abiotic surfaces in CFT073 and various UPEC strains. In addition, UpaG expression resulted in the adhesion of CFT073 to human bladder epithelial cells, with specific affinity to fibronectin and laminin. Prevalence analysis revealed thatupaGis strongly associated withE. colistrains from the B2 and D phylogenetic groups, while deletion ofupaGhad no significant effect on the ability of CFT073 to colonize the mouse urinary tract. Thus, UpaG is a novel trimeric AT adhesin fromE. colithat mediates aggregation, biofilm formation, and adhesion to various ECM proteins.
Formate Acts as a Diffusible Signal To InduceSalmonellaInvasion
Authors: Huang Yanyan , Suyemoto Mitsu , Garner Cherilyn D. , Cicconi Kellie M. , Altier Craig 
Published: April 2008

ABSTRACTTo infect an animal host,Salmonella entericaserovar Typhimurium must penetrate the intestinal epithelial barrier. This process of invasion requires a type III secretion system encoded withinSalmonellapathogenicity island I (SPI1). We found that a mutant with deletions of the acetate kinase and phosphotransacetylase genes (ackA-pta) was deficient in invasion and SPI1 expression but that invasion gene expression was completely restored by supplying medium conditioned by growth of the wild-type strain, suggesting that a signal produced by the wild type, but not by theackA-ptamutant, was required for invasion. This mutant also excreted 68-fold-less formate into the culture medium, and the addition of sodium formate to cultures restored both the expression of SPI1 and the invasion of cultured epithelial cells by the mutant. The effect of formate was pH dependent, requiring a pH below neutrality, and studies in mice showed that the distal ileum, the preferred site ofSalmonellainvasion in this species, had the appropriate formate concentration and pH to elicit invasion, while the cecum contained no detectable formate. Furthermore, we found that formate affected the major regulators of SPI1,hilAandhilD, but that the primary routes of formate metabolism played no role in its activity as a signal.
Functional Analysis of the Protein Machinery Required for Transport of Lipopolysaccharide to the Outer Membrane of
Escherichia coli
Authors: Sperandeo Paola , Lau Fion K. , Carpentieri Andrea , De Castro Cristina , Molinaro Antonio , Dehò Gianni , Silhavy Thomas J. , Polissi Alessandra 
Published: April 2008

ABSTRACT
Lipopolysaccharide (LPS) is an essential component of the outer membrane (OM) in most gram-negative bacteria, and its structure and biosynthetic pathway are well known. Nevertheless, the mechanisms of transport and assembly of this molecule at the cell surface are poorly understood. The inner membrane (IM) transport protein MsbA is responsible for flipping LPS across the IM. Additional components of the LPS transport machinery downstream of MsbA have been identified, including the OM protein complex LptD/LptE (formerly Imp/RlpB), the periplasmic LptA protein, the IM-associated cytoplasmic ATP binding cassette protein LptB, and LptC (formerly YrbK), an essential IM component of the LPS transport machinery characterized in this work. Here we show that depletion of any of the proteins mentioned above leads to common phenotypes, including (i) the presence of abnormal membrane structures in the periplasm, (ii) accumulation of de novo-synthesized LPS in two membrane fractions with lower density than the OM, and (iii) accumulation of a modified LPS, which is ligated to repeating units of colanic acid in the outer leaflet of the IM. Our results suggest that LptA, LptB, LptC, LptD, and LptE operate in the LPS assembly pathway and, together with other as-yet-unidentified components, could be part of a complex devoted to the transport of LPS from the periplasmic surface of the IM to the OM. Moreover, the location of at least one of these five proteins in every cellular compartment suggests a model for how the LPS assembly pathway is organized and ordered in space.
Conserved Residues Asp16 and Pro24 of TnaC-tRNA
Pro
Participate in Tryptophan Induction of
tna
Operon Expression
Authors: Cruz-Vera Luis R. , Yanofsky Charles 
Published: April 2008

ABSTRACT

In
Escherichia coli
, interactions between the nascent TnaC-tRNA
Pro
peptidyl-tRNA and the translating ribosome create a tryptophan binding site in the ribosome where bound tryptophan inhibits TnaC-tRNA
Pro
cleavage. This inhibition delays ribosome release, thereby inhibiting Rho factor binding and action, resulting in increased
tna
operon transcription. Replacing Trp12 of TnaC with any other amino acid residue was previously shown to prevent tryptophan binding and induction of
tna
operon expression. Genome-wide comparisons of TnaC amino acid sequences identify Asp16 and Pro24, as well as Trp12, as highly conserved TnaC residues. Replacing these residues with other residues was previously shown to influence tryptophan induction of
tna
operon expression. In this study, in vitro analyses were performed to examine the potential roles of Asp16 and Pro24 in
tna
operon induction. Replacing Asp16 or Pro24 of TnaC of
E. coli
with other amino acids established that these residues are essential for free tryptophan binding and inhibition of TnaC-tRNA
Pro
cleavage at the peptidyl transferase center. Asp16 and Pro24 are in fact located in spatial positions corresponding to critical residues of AAP, another ribosome regulatory peptide. Sparsomycin-methylation protection studies further suggested that segments of 23S RNA were arranged differently in ribosomes bearing TnaCs with either the Asp16Ala or the Pro24Ala change. Thus, features of the amino acid sequence of TnaC of the nascent TnaC-tRNA
Pro
peptidyl-tRNA, in addition to the presence of Trp12, are necessary for the nascent peptide to create a tryptophan binding/inhibition site in the translating ribosome.
The ArgP Protein Stimulates the
Klebsiella pneumoniae gdhA
Promoter in a Lysine-Sensitive Manner
Authors: Goss Thomas J. 
Published: April 2008

ABSTRACT

The lysine-sensitive factor that binds to the upstream region of the
Klebsiella pneumoniae gdhA
promoter and stimulates
gdhA
transcription during growth in minimal medium has been proposed to be the
K. pneumoniae
ArgP protein (M. R. Nandineni, R. S. Laishram, and J. Gowrishankar, J. Bacteriol. 186:6391-6399, 2004). A knockout mutation of the
K. pneumoniae argP
gene was generated and used to assess the roles of exogenous lysine and
argP
in the regulation of the
gdhA
promoter. Disruption of
argP
reduced the strength and the lysine-dependent regulation of the
gdhA
promoter. Electrophoretic mobility shift assays using crude extracts prepared from wild-type and
argP
-defective strains indicted the presence of an
argP
-dependent factor whose ability to bind the
gdhA
promoter was lysine sensitive. DNase I footprinting studies using purified
K. pneumoniae
ArgP protein indicated that ArgP bound the region that lies approximately 50 to 100 base pairs upstream of the
gdhA
transcription start site in a manner that was sensitive to the presence of lysine. Substitutions within the region bound by ArgP affected the binding of ArgP to the
gdhA
promoter region in vitro and the
argP
-dependent stimulation of the
gdhA
promoter in vivo. These observations suggest that elevated intracellular levels of lysine reduce the affinity of ArgP for its binding site at the
gdhA
promoter, preventing ArgP from binding to and stimulating transcription from the promoter in vivo.
YscP and YscU Switch the Substrate Specificity of the
Yersinia
Type III Secretion System by Regulating Export of the Inner Rod Protein YscI
Authors: Wood Sarah E. , Jin Jin , Lloyd Scott A. 
Published: April 2008

ABSTRACT

Pathogenic yersiniae utilize a type III secretion system to inject antihost factors, called Yops, directly into the cytosol of eukaryotic cells. The Yops are injected via a needle-like structure, comprising the YscF protein, on the bacterial surface. While the needle is being assembled, Yops cannot be secreted. YscP and YscU switch the substrate specificity of the secretion system to enable Yop export once the needle attains its proper length. Here, we demonstrate that the inner rod protein YscI plays a critical role in substrate specificity switching. We show that YscI is secreted by the type III secretion system and that YscI secretion by a
yscP
mutant is abnormally elevated. Furthermore, we show that mutations in the cytoplasmic domain of YscU reduce YscI secretion by the
yscP
null strain. We also demonstrate that mutants expressing one of three forms of YscI (those with mutations Q84A, L87A, and L96A) secrete substantial amounts of Yops yet exhibit severe defects in needle formation. In the absence of YscP, mutants with the same changes in YscI assemble needles but are unable to secrete Yops. Together, these results suggest that the formation of the inner rod, not the needle, is critical for substrate specificity switching and that YscP and YscU exert their effects on substrate export by controlling the secretion of YscI.
ApoFnr Binds as a Monomer to Promoters Regulating the Expression of Enterotoxin Genes of
Bacillus cereus
Authors: Esbelin Julia , Jouanneau Yves , Armengaud Jean , Duport Catherine 
Published: April 2008

ABSTRACT

Bacillus cereus
Fnr is a member of the Crp/Fnr (cyclic AMP-binding protein/fumarate nitrate reduction regulatory protein) family of helix-turn-helix transcriptional regulators. It is essential for the expression of
hbl
and
nhe
enterotoxin genes independently of the oxygen tension in the environment. We studied aerobic Fnr binding to target sites in promoters regulating the expression of enterotoxin genes.
B. cereus
Fnr was overexpressed and purified as either a C-terminal His-tagged (Fnr
His
) fusion protein or an N-terminal fusion protein tagged with the
Strep
-tag (IBA BioTAGnology) (
Strep
Fnr). Both recombinant Fnr proteins were produced as apoforms (clusterless) and occurred as mixtures of monomers and oligomers in solution. However, apoFnr
His
was mainly monomeric, while apo
Strep
Fnr was mainly oligomeric, suggesting that the His-tagged C-terminal extremity may interfere with oligomerization. The oligomeric state of apo
Strep
Fnr was dithiothreitol sensitive, underlining the importance of a disulfide bridge for apoFnr oligomerization. Electrophoretic mobility shift assays showed that monomeric apoFnr, but not oligomeric apoFnr, bound to specific sequences located in the promoter regions of the enterotoxin regulators
fnr
,
resDE
, and
plcR
and the structural genes
hbl
and
nhe
. The question of whether apoFnr binding is regulated in vivo by redox-dependent oligomerization is discussed.
The Critical Role ofembCinMycobacterium tuberculosis
Authors: Goude Renan , Amin Anita G. , Chatterjee Delphi , Parish Tanya 
Published: April 2008

ABSTRACTArabinan polymers are major components of the cell wall inMycobacterium tuberculosisand are involved in maintaining its structure, as well as playing a role in host-pathogen interactions. In particular, lipoarabinomannan (LAM) has multiple immunomodulatory effects. In the nonpathogenic speciesMycobacterium smegmatis, EmbC has been identified as a key arabinosyltransferase involved in the incorporation of arabinose into LAM, and anembCmutant is viable but lacks LAM. In contrast, we demonstrate here that inM. tuberculosis,embCis an essential gene under normal growth conditions, suggesting a more crucial role for LAM in the pathogenic mycobacteria.M. tuberculosisEmbC has an activity similar to that ofM. smegmatisEmbC, since we were able to complement anembCmutant ofM. smegmatiswithembCMtb, confirming that it encodes a functional arabinosyltransferase. In addition, we observed that the size of LAM produced inM. smegmatiswas dependent on the level of expression ofembCMtb. Northern analysis revealed thatembCis expressed as part of a polycistronic message encompassingembCand three upstream genes. The promoter region for this transcript was identified and found to be up-regulated in stationary phase but down-regulated during hypoxia-induced nonreplicating persistence. In conclusion, we have identified one of the key genes involved in LAM biosynthesis inM. tuberculosisand confirmed its essential role in this species.
Identification of a Novel Trimeric Autotransporter Adhesin in the Cryptic Genospecies of
Haemophilus
Authors: Sheets Amanda J. , Grass Susan A. , Miller Sara E. , St. Geme Joseph W. 
Published: April 2008

ABSTRACT

Haemophilus
biotype IV strains belonging to the recently recognized
Haemophilus
cryptic genospecies are an important cause of maternal genital tract and neonatal systemic infections and initiate infection by colonizing the genital or respiratory epithelium. To gain insight into the mechanism of
Haemophilus
cryptic genospecies colonization, we began by examining prototype strain 1595 and three other strains for adherence to genital and respiratory epithelial cell lines. Strain 1595 and two of the three other strains demonstrated efficient adherence to all of the cell lines tested. With a stably adherent variant of strain 1595, we generated a Mariner transposon library and identified 16 nonadherent mutants. All of these mutants lacked surface fibers and contained an insertion in the same open reading frame, which encodes a 157-kDa protein designated Cha for
c
ryptic
h
aemophilus
a
dhesin. Analysis of the predicted amino acid sequence of Cha revealed the presence of an N-terminal signal peptide and a C-terminal domain bearing homology to YadA-like and Hia-like trimeric autotransporters. Examination of the C-terminal 120 amino acids of Cha demonstrated mobility as a trimer on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the capacity to present the passenger domain of the Hia trimeric autotransporter on the bacterial surface. Southern analysis revealed that the gene that encodes Cha is conserved among clinical isolates of the
Haemophilus
cryptic genospecies and is absent from the closely related species
Haemophilus influenzae
. We speculate that Cha is important in the pathogenesis of disease due to the
Haemophilus
cryptic genospecies and is in part responsible for the apparent tissue tropism of this organism.
Mutations in thetacFGene of Clinical Strains and Laboratory Transformants ofStreptococcus pneumoniae:Impact on Choline Auxotrophy and Growth Rate
Authors: González Ana , Llull Daniel , Morales María , García Pedro , García Ernesto 
Published: April 2008

ABSTRACTThe nutritional requirement thatStreptococcus pneumoniaehas for the aminoalcohol choline as a component of teichoic and lipoteichoic acids appears to be exclusive to this prokaryote. A mutation in thetacFgene, which putatively encodes an integral membrane protein (possibly, a teichoic acid repeat unit transporter), has been recently identified as responsible for generating a choline-independent phenotype ofS. pneumoniae(M. Damjanovic, A. S. Kharat, A. Eberhardt, A. Tomasz, and W. Vollmer, J. Bacteriol. 189:7105-7111, 2007). We now report thatStreptococcus mitiscan grow in choline-free medium, as previously illustrated forStreptococcus oralis. While we confirmed the finding by Damjanovic et al. of the involvement of TacF in the choline dependence of the pneumococcus, the genetic transformation ofS. pneumoniaeR6 by usingS. mitisSK598 DNA and several PCR-amplifiedtacFfragments suggested that a minimum of two mutations were required to confer improved fitness to choline-independentS. pneumoniaemutants. This conclusion is supported by sequencing results also reported here that indicate that a spontaneous mutant ofS. pneumoniae(strain JY2190) able to proliferate in the absence of choline (or analogs) is also a double mutant for thetacFgene. Microscopic observations and competition experiments during the cocultivation of choline-independent strains confirmed that a minimum of two amino acid changes were required to confer improved fitness to choline-independent pneumococcal strains when growing in medium lacking any aminoalcohol. Our results suggest complex relationships among the different regions of the TacF teichoic acid repeat unit transporter.
Patellofemoral pain syndrome: a review on the associated neuromuscular deficits and current treatment options
Authors: Fagan V , Delahunt E 
Published: April 2008

Background:Patellofemoral pain syndrome (PFPS) is a common clinical presentation. Various neuromuscular factors have been reported to contribute to its aetiology.Study design:Systematic reviewMethods:A literature search was carried out from 1998 up to December 2007. Eligible studies were those that: (1) examined the effects of hip strengthening in subjects with PFPS; (2) examined the effects of physiotherapy treatment aimed at restoring muscle balance between the vastus medialis oblique (VMO) and vastus lateralis (VL) in subjects with PFPS; (3) examined the effect of taping on electromyogram (EMG) muscle amplitude in subjects with PFPS; and (4) compared the effects of open versus closed kinetic chain exercises in the treatment of subjects with PFPS.Results and conclusion:No randomised controlled trials exist to support the use of hip joint strengthening in subjects with PFPS. Physiotherapy treatment programmes appear to be an efficacious method of improving quadriceps muscle imbalances. Further studies are required to determine the true efficacy of therapeutic patellar taping. Both open and closed kinetic chain exercises are appropriate forms of treatment for subjects with PFPS.