bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variable expression of the Opc outer membrane protein in Neisseria meningitidis is caused by size variation of a promoter containing poly‐cytidine
Authors: Sarkari Jasmine , Pandit Niketan , Moxon E. Richard , Achtman Mark 
Published: October 2006

SummaryOpa proteins of Neisseria meningitidis exhibit translational phase variation via addition or deletion of repetitive coding repeat units within the DNA encoding the protein leader sequence. In contrast, Opc phase variation is the result of transcriptional regulation. Transcription starts 13 nucleotides after the ‐10 region of an unusual promoter sequence containing a variable number of contiguous cytidine residues and lacking a ‐ 35 region. Efficient expression of Opc occurred in strains with 12 to 13 cytidine residues, intermediate expression in strains with 11 or 14 residues and no expression with ≤ 10 or ≥ 15 residues. This unusual regulation may have evolved because the Opc protein enables meningococcal invasion and is immunogenic.
Cloning and molecular characterization of a Legionella pneumophila gene induced by intracellular infection and by various in vitro stress conditions
Authors: Kwaik Yousef Abu , Engleberg N. Cary 
Published: October 2006

SummaryThe synthesis of a global stress protein (GspA) of Legionella pneumophila is induced in the intracellular environment of the phagocytic ceil and by various in vitro stress stimuli. We used techniques of reverse genetics to isolate the gspA gene from a genomic library of L. pneumophila. Sequence analysis of approximately 1700 bp of a representative clone (pBSP1) showed the presence of two open reading frames (ORFs). 0RF1 encoded for a polypeptide with an inferred molecular mass of 19kDa and an iso‐electric point of 6.1. These predictions correlated with the migration of the GspA protein on two‐dimensional SDS‐polyacrylamide gels. The predicted amino acid sequence of the GspA protein was identicai to 22/23 residues of the N‐terminal amino acid sequence derived by Edman degradation of the purified protein. The GspA protein was 41.3% and 36.5% identical to the 16 kDa ibpA and IbpB heat‐shock proteins, respectively, of Escherichia coli. Primer extension from mRNA isolated from L. pneumophila showed that transcription of the gspA gene was controlled by two overlapping promoters. One of the promoters was a σ70 promoter, while the other was a heat‐shock promoter and was regulated by the σ32 transcription factor in E. coli. Northern biol analysis showed that the level of gspA mRNA was elevated 3.4‐, 5.0‐ and 6.7‐foid after exposure of L. pneumophila to heat shock, oxidative stress and osmotic shock, respectiveiy. The gspA gene was conserved among 13 serogroups of L pneumophila. Our data showed that the gspA gene of L. pneumophila, which is induced by intracellular infection and by various stress stimuli, is controlled transcriptionally by two overlapping and separately regulated promoters.
The pesticin receptor of Yersinia enterocolitica: a novel virulence factor with dual function
Authors: Rakin Alexander , Saken Elisabeth , Harmsen Dag , Heesemann Jürgen 
Published: October 2006

SummaryThe iron‐repressible outer membrane protein FyuA of Yersinia enterocolitica operates as a receptor with dual function: (i) as a receptor for the Y. pestis bacterlocin pesticin, and (ii) as a receptor for yersiniabactin, a siderophore that is produced by mouse‐viruient Y. enterocolitica strains of biogroup IB. Cloning of the FyuA‐encoding gene was achieved by mobilization of a genomic cosmid library of the pesticin‐sensitive and mouse‐virulent Y. enterocolitica O:8 strain WA into the pesticin‐reslstant WA fyuA mutant and subsequent in vivo selection of transconjugants for the ability to survive and multiply in mice (phenotype mouse viruience). The reisolated transconjugants which survived in mice for 3d harboured a unique cosmid and phenotypicaity were pesticin sensitive. From this cosmid a 2650 bp SalI‐PstI fragment conferring pesticin sensitivity was subcioned. Sequencing of this DNA fragment revealed a single open reading frame of 2022 bp, which encodes a deduced polypeptide of 673 amino acids with a predicted molecular mass of 73 677 Da. Cleavage of a putative signal sequence composed of 22 amino acids should lead to a mature protein of 651 amino acids with a molecular mass of 71 368 Da. The open reading frame is preceded by a sequence which shares homoiogy with the postulated consensus Fur iron‐repressor protein‐binding site. FyuA shows homology to other iron‐regulated TonB‐dependent outer membrane proteins with receptor functions (e.g. BtuB, CirA, FepA, lutA, FhuA, FoxA, FcuA). On the basis of multiple alignment of amino acid sequences of FyuA and other TonB‐dependent receptors, a phylogenetic tree was constructed, demonstrating that FyuA probably belongs to the citrate subfamily or represents a new subfamily of TonB‐dependent receptors. Moreover, by complementation of the WA fyuA mutant by the cioned fyuA gene.
The dps promoter is activated by OxyR during growth and by IHF and σs in stationary phase
Authors: Altuvia Shoshy , Almiron Marta , Huisman Gjalt , Kolter Roberto , Storz Gisela 
Published: October 2006

SummaryDps is a non‐specific DNA‐binding protein abundant In starved Escherichia coli cells and is important for the defence against hydrogen peroxide. We found that dps mRNA levels are controlled by rpoS‐encoded σs, the transcriptional activator OxyR and the histone‐like IHF protein, in exponentially growing cells, dps is induced by treatment with hydrogen peroxide in an OxyR‐dependent manner. This OxyR‐dependent induction occurs only during log phase, although the OxyR protein is present in stationary phase, in the stationary phase cells, dps is expressed in a σs ‐ and IHF‐dependent manner. The purified OxyR and IHF proteins are also shown to bind upstream of the dps promoter. Our results suggest that the dps promoter is recognized by both σ70‐holoenzyme and σs‐holoenzyme, since OxyR acts through σ70 and the starts of the OxyR‐ and σs‐dependent transcripts are identical.
Activation of a vmp pseudogene in Borrella hermsii: an alternate mechanism of antigenic variation during relapsing fever
Authors: Restrepo B. I. , Carter C. J. , Barbour A. G. 
Published: October 2006

SummaryThe relapsing fever agent, Borrella hermsii, undergoes multiphasic antigenic variation to evade its host's immune response. A frequently observed switch is serotype 7 to 26. Unlike silent vmp genes previously characterized, the transcriptionally silent vmp26 sequence was a pseudogene in lacking a start codon. In serotype 7 the location of the silent vmp26 sequence just downstream of vmp7 on the expression plasmid, as well as on the silent plasmid, was also unique. The demonstration of a predicted circular recombination product in serotype 7 but not serotype 21 populations indicates that the pseudogene was activated by an intramolecular recombination producing a deletion of DNA between 20‐nucleotide direct repeats in vmp7 and Ψvmp26.
Cloning, sequencing, and characterization of multicopy suppressors of a mukB mutation in Escherichia coli
Authors: Yamanaka Kunitoshl , Mitani Tadao , Ogura Teru , Niki Hironorl , Hiraga Sota 
Published: October 2006

SummaryThe mukB gene codes for a 177kDa protein, which might be a candidate for a force‐generating enzyme in chromosome positioning in Escherichia coli. The mukB106 mutant produces normal‐sized, anucleate cells and shows a temperature‐sensitive colony formation. To Identify proteins interacting with the MukB protein, we isolated three multicopy suppressors (msmA, msmB, and msmC) to the temperature‐sensitive colony formation of the mukB106 mutation. The msmA gene, which could not suppress the production of anucleate cells, was found to be identical to the dksA gene. The msmB and msmC genes suppressed the production of anucleate cells as well as the temperature‐sensitive colony formation. However, none of them couid suppress both phenotypes in a mukB null mutation. DNA sequencing revealed that the msmB gene was identicai to the cspC gene and that the msmC gene had not been described before. A homology search revealed that the amino acid sequences of both MsmB and MsmC possessed high similarity to proteins containing the cold‐shock domain, such as CspA of E. coliand the Y‐box binding proteins of eukaryotes; this suggests that MsmB and MsmC might be DNA‐binding proteins that recognize the CCAAT sequence. Hence, the msmB and msmC genes were renamed cspC and cspE, respectively. Possible mechanisms for suppression of the mukB106 mutation are discussed.
The purified SoxABCD quinol oxidase complex of Sulfolobus acidocaldarius contains a novel haem
Authors: Lübben Mathias , Warne Antony , Albracht Simon P. J. , Saraste Matti 
Published: October 2006

SummaryA respiratory quinol oxidase complex that is encoded by the soxABCD operon has been purified from the thermoacidophilic archaeon Sulfolobus acidocaldarius. The enzyme was solubilized with dodecyl maltoside and purified in the presence of this detergent and ethylene glycol. The complex is hydro‐dynamically homogeneous and contains at least five different polypeptides. In addition to the major subunits SoxA, SoxB and SoxC, it has two small polypeptides. One of these is the translation product of a short open reading frame (now called the soxD gene) at the end of the operon. The optical and electron paramagnetic resonance spectra of the SoxABCD compiex have been characterized. It probably contains four A‐type haems which are bound to SoxB and SoxC. The structure of these haems is not identical to haem A. The novel haem Aa has a 2‐hydroxyethyl geranylgeranyl in position 2 of the porphyrin ring whereas haem A has the related farnesyl‐containing side‐chain.
Identification and characterization of hitherto unknown Mycoplasma pneumoniae proteins
Authors: Proft Thomas , Herrmann Richard 
Published: October 2006

SummaryEleven hitherto unknown Mycoplasma pneumoniae proteins were identified and characterized with respect to their size and subcellular location. This was carried out through the construction of in vitro gene fusions between a modified mouse dehydrofolate reductase (dhfr) gene and selected regions (cosmid clones) of the M. pneumoniae genome and expressing them in Escherichia coli. Positive clones were identified using antibodies against specific fractions of M. pneumoniae. The deduced protein sequences of 11 out of 30 clones did not show significant homologies to known proteins in protein databank searches. Monospecific antibodies against these 11 fusion proteins were used to determine the size and cellular location of the corresponding M. pneumoniae proteins by immunoscreening Western blots of SDS‐acrylamide gels from M. pneumoniae cell extracts.
Multiplicity of genes encoding secreted aspartic proteinases in Candida species
Authors: Monod Michel , Togni Giuseppe , Hube Bernhard , Sanglard Dominique 
Published: October 2006

SummaryThe secreted aspartic proteinases (SAP) of Candida sp. are presumed to be potential virulence factors. In the opportunistic pathogen Candida albicans the proteinase genes identified to date, SAP1, SAP2, SAP3 and SAP4, constitute a multigene family. Before addressing the possible role of each proteinase in virulence, we sought to isolate all the members of this multigene family by screening a genomic library with a SAP1 probe for additional C. albicans SAP genes using low‐stringency hybridization conditions. Three putative new members, SAP5, SAP6 and SAP7 were isolated and sequenced. The N‐terminal segments of the deduced amino acid sequences of SAP5 and SAP6 contained secretion signal sequences similar to those of other Candida SAPs. Upon comparison and alignment with the other reported SAP amino acid sequences, SAP7 is not only the most divergent protein but also exhibits a much longer putative pro‐sequence with a single Lys‐Lys putative processing site. Using SAP1 to SAP7 as probes, the overall number of SAP genes in C. albicans was tentatively estimated by low‐stringency hybridization to EcoRI‐digested genomic DNA. While each isolated SAP gene could be assigned to distinct EcoRI bands, the existence of two additional genes not isolated after screening of the C. albicans gene library was inferred. Furthermore, evidence was obtained for the existence of SAP muttigene families in other Candida species such as C. tropicalis, C. parapsilosis and C. guiller‐mondii.
Micro Review tRNA‐dircted transcription antitermination
Authors: Henkin Tina M. 
Published: October 2006

SummaryAt least 18 aminoacyl‐tRNA synthetase and amino acid biosynthesis genes in several Gram‐positive genera appear to be regulated by a common transcription anti‐termination mechanism. Each gene is induced by limitation for the appropriate amino acid, and not by general amino acid limitation. The mRNA leader regions of these genes exhibit extensive structural conservation. haracterization of the Bacillus subtilis tyrS gene revealed that uncharged tyrosyl‐tRNA promotes readthrough of a leader‐region terminator; a conformational switch in the leader mRNA between a terminator structure and an antiterminator structure is postulated to mediate antitermination. Two sites of interaction between the tRNA and the leader have been identified by genetic analysis: the tRNA anti‐codon interacts with a single codon displayed at a precise position in the leader‐region structure, and the acceptor end of the tRNA interacts with a side‐bulge on the antiterminator.
Bees aren't the only ones: swarming in Gram‐negative bacteria
Authors: Harshey Rasika M. 
Published: October 2006

SummarySwarming is a form of active surface motility that is widespread among flagellated. Gram–negative bacteria. In the laboratory, growth of the bacteria on certain agar surfaces leads to induction of the differentiated swarmer‐cell state. Swarmer cells are generally long and multinucleate, always hyperflagellated, and can move rapidly over the agar surface in a coordinated manner. Some swarm colonies exude large amounts of ‘slime’, which could be essential for promoting intimate cell–cell contacts during swarming. There is evidence that the differentiated swarmer‐cell stage facilitates pathogenic associations with host tissue. Almost nothing is known about the molecular signalling mechanism of surface sensing. Increased viscosity appears to be sensed by several bacteria, but other environmental cues, specific to each bacterium, are also important. In organisms in which swarming motility has been studied in some detail, the chemotaxis system has been shown to play an important rote. The recent discovery of swarming motility in two genetically well‐characterized organisms –Escherichia coli and Salmonella typhimurium– should lead to rapid progress in understanding this process.
The actin‐based motility of the facultative intracellular pathogen Listeria monocytogenes
Authors: Cossart Pascale , Kocks Christine 
Published: October 2006

SummaryThe Gram‐positive bacterium Listeria monocytogenes is a facultative intracellular parasite that invades and multiplies within diverse eukaryotic cell types. An essential pathogenicity determinant is its ability to move in the host cell cytoplasm and to spread within tissues by directly passing from one cell to another. The propulsive force for intracellular movement is thought to be generated by continuous actin assembly at the rear end of the bacterium. Moving bacteria that reach the plasma membrane induce the formation of long membranous protrusions that are internalized by neighbouring cells, thus mediating the spread of infection. The unrelated pathogens Shigella and Rickettsia use a similar process of actin‐based motility to disseminate in infected tissues. This review focuses on the bacterial and cellular factors involved in the actin‐based motility of L monocytogenes.
Sequence changes in the pilus subunit lead to tropism variation of Neisseria gonorrhoeae to human tissue
Authors: Jonsson Ann‐Beth , Ilver Dag , Falk Per , Pepose Jay , Normark Staffan 
Published: October 2006

SummaryPili of Neisseria gonorrhoeae are correlated with Increased bacterial attachment to epithelial cells and undergo both phase and antigenic variation. Phase variation of gonococcal pili can be brought about by recombination events in the pilin structural gene, pilE, or by the on/off switch in expression of PilC, a pilus biogenesis protein for which two loci exist. We have studied the binding to epithelial cell lines and to fixed tissue sections of N. gonorrhoeae MS11 derivatives and mutants carrying structurally defined PilE and PilC proteins, in situ binding studies of N. gonorrhoeae to formalin‐fixed tissue sections resulted in a binding pattern similar to that obtained using viable epithelial cell lines of different origin. Piliated gonococcal clones, containing different pilE sequences, varied dramatically from one another in their efficiencies at binding to corneal and conjunctival tissue, but bound equally well to cervical and endometrial tissues. Further, the binding data suggested that PJIC expression by itself, i.e. without pili, cannot confer bacterial binding and that expression of either PilC1 or PiiC2 does not confer different binding properties to the bacterial cells. Possible receptors for piliated gonococci were expressed in human tissues, such as cervix, endometrium, cornea, intestine, stomach, mid‐brain and meninges, but not in human kidney. Pretreatment of the target tissues with Proteinase K decreased the gonococcal binding dramatically, whereas pretreatment with neuraminidase and meta‐periodate, which cleave carbon‐carbon linkages between vicinal hydroxyl groups in carbohydrates, did not affect attachment of gonococci. These data argue that pilus‐dependent attachment of N. gonorrhoeae to human tissue may be mediated by a eukaryotic receptor having protein characteristics, and that the pilus subunit sequence may play an important role in the interaction with human cornea.
The rfb locus from Pseudomonas aeruginosa strain PA103 promotes the expression of O antigen by both LPS‐rough and LPS‐smooth isolates from cystic fibrosis patients
Authors: Evans David J. , Pier Gerald B. , Coyne Michael J. , Goldberg Joanna B. 
Published: October 2006

SummaryStrains of Pseudomonas aeruginosa initially isolated from patients with cystic fibrosis (CF) often express a smooth lipopolysaccharide (LPS) containing many long O side‐chain antigens, but once a chronic infection is established, strains recovered from these patients express little or no LPS O antigen. The genetic basis for this loss of O antigen expression by P. aeruginosa CF isolates is unknown. We report here that 20 CF isoiates of P. aeruginosa, 13 of which are LPS‐rough, were each capable of expressing serogroup 011 antigen when provided with the rfb iocus from P. aeruginosa serogroup 011 strain PA103 on the recombinant plasmid pLPS2. Eight of the thirteen LPS‐rough isolates co‐expressed another, presumably endogenous, O antigen when they contained pLPS2. Different subcloned regions of pLPS2 complemented distinct strains to restore endogenous O antigen expression. These data suggest that the loss of O antigen expression by P. aeruginosa CF isolates results from alterations specific to the rfb region, and is not due to mutations involving other loci or ancillary LPS genes.
Transmembrane signal transduction by the Escherichia coli osmotic sensor, EnvZ: intermolecular complementation of transmembrane signalling
Authors: Tokishita Shin‐ichi , Mizuno Takeshi 
Published: October 2006

SummaryThe Escherichia coli regulatory proteins, EnvZ and OmpR, are crucially involved in expression of the outer membrane proteins OmpF/OmpC in response to the medium osmolarity. The EnvZ protein is presumably a membrane‐located osmotic sensor (or signal transducer), which exhibits both kinase and phosphatase activities specific for the OmpR protein. To examine the functional importance of the membrane‐spanning segments (named TM1 and TM2) of EnvZ molecules in transmembrane signalling, a set of EnvZ mutants, each having amino acid substitutions within the membrane‐spanning regions, was characterized in terms of both their in vivo phenotype and in vitro catalytic activities. One of them, characterized further, has an amino acid change (Pro‐41 to Ser or Leu) In TM1, and appeared to be defective in its phosphatase activity but not in its kinase activity. This EnvZ mutant conferred a phenotype of OmpF−/OmpC‐constitutive. For this EnvZ(P41S or P41L) mutant, a set of intragenic suppressors, each exhibiting a wild‐type phenotype of OmpF+/OmpC+, was isolated. These suppresor mutants were revealed to have an additional amino acid change within either TM1 or TM2. Furthermore, they exhibited restored phosphatase activity (i.e., both kinase+ and phosphatase+ activities). It was further demonstrated that one of the suppressors, EnvZ(Arg‐180 to Trp in TM2), was able to suppress the defects in both the in vivo phenotype and the in vitro catalytic activities caused by EnvZ(P41S), through intermolecular complementation. These results are best interpreted as meaning that an intimate intermolecular interaction between the membrane–spanning segments of EnvZ is crucial for transmembrane signalling per se in response to an external osmotic stimulus.
The protein HU can displace the LexA repressor from its DNA‐binding sites
Authors: Preobrajenskaya Olga , Boullard Annie , Boubrik Fatima , Schnarr Manfred , Rouvière‐Yaniv Josette 
Published: October 2006

SummaryThe major bacterial histone‐like protein HU is a small, basic, dimeric protein composed of two closely related subunits. HU is involved in several processes in the bacterial cell such as the initiation of replication, transposition, gene inversion and cell division. It has been suggested that HU could introduce structural changes to the DNA which would facilitate or inhibit the binding of regulatory proteins to their specific sites. In this study we investigated the effect of HU on the binding of LexA protein, the regulator of SOS functions, to three of its specific binding sites. We show that HU can displace LexA from its binding sites on the operators of the lexA, recA and sfiA genes. The lexA operator was the most sensitive while the higher affinity sfiA operator was the least sensitive. Since HU, like its homologue IHF, probably binds DNA in the minor groove we tested the effect of distamycin, a drug which binds to the minor groove, on LexA binding. Like HU, this drug disrupted LexA–operator complexes. These results suggest that distortion of the minor groove of the lexA operators excludes the binding of the repressor to the major groove.
Neither absence nor excess of λ O initiator‐digesting ClpXP protease affects λ plasmid or phage replication in Escherichia coli
Authors: Szalewska Agnieszka , Wȩgrzyn Grzegorz , Taylor Karol 
Published: October 2006

SummaryOwing to rapid proteolysis of the coliphage λ‐coded initiator protein, λ O, this protein is considered to carry a rate–limiting step in λ DNA replication. The discovery of ClpXP protease responsible for λ O protein turnover allowed an opportunity to verify this hypothesis. However, neither absence nor excess of this protease significantly affected the transformation efficiency and copy number of λ plasmid, or the Kinetics of the λ phage growth. These results are also incompatible with the hypothesis that the stabilization of λ O plays a role in the switch from early (circle‐to‐circle) to late (rolling‐circle) λ phage DNA replication. Tran‐scriptional activation of oriλ probably assisted by the Escherichia coli DnaA function, remains as the possible rate‐limiting step in λ DNA replication.