bluuebunny/crossref_metadata_2025_split huggingface dataset:
The absence of a surface protease, OmpT, determines the intercellular spreading ability of Shigella: the relationship between the ompT and kcpA loci
Authors: Nakata N. , Tobe T. , Fukuda I. , Suzuki T. , Komatsu K. , Yoshikawa M. , Sasakawa C. 
Published: October 2006

SummaryA large plasmid‐encoded protein, VirG, on the bacterial surface is essential for the spreading of Shigella by eliciting polar deposition of filamentous actin In the cytoplasm of epithelial cells. VirG expression from the large plasmid is diminished greatly when it is introduced into Escherichia coli K‐12 from Shigella. In an attempt to identify factors affecting VirG expression, we found that the absence of the ompT gene, encoding outer membrane protease OmpT, restored full production of VirG protein to E. coli K‐12. Conversely, upon introduction of the ompT gene of E. coii K‐12 into Shigella, spreading ability was completely abolished, probably because of the proteolytic degradation of VirG protein by OmpT. Analysis of the DNA sequence of the ompT region indicated that the absence of the ompT gene occurred in Shigella and enteroinvasive E. coli strains, and that the absent DNA segment corresponded to a remnant lambdoid phage structure found in E. coli K‐12, which encompasses a 21 kb DNA segment spanning from argU through to the ompT genes. Since ompT is located near purE in E. coli K‐12 and a virulence locus for provoking keratocon‐junctivitis in the eyes of guinea‐pigs, named kcpA is located near purE in S. fiexnerl, and the two loci are involved in VirG expression, the KcpA∼ mutants of S. flexneri 2a constructed were examined for correlation between acquisition of ompT and VirG degradation. Our data suggest that the previous recognition of a kcpA locus in S. flexneri is the result of transfer of the ompr gene from E. coli K‐12, giving rise to a KcpA phenotype. These results indicate that the lack of OmpT protease confers upon Shigella the ability to spread into adjacent epithelial cells.
Identification of a novel gene, dep, associated with depolymerization of the capsular polymer in Bacillus anthracis
Authors: Uchida I. , Makino S. , Sasakawa C. , Yoshikawa M. , Sugimoto C. , Terakado N. 
Published: October 2006

Summary Bacillus anthracis produces a gamma‐linked poly‐D‐glutamic acid capsule that is essential for virulence. A 6.2 kb fragment of B. anthracis DNA (cap), when present in Escherichia coli, produces a capsular polymer that is immunologically identical to that produced by B. anthracis. By immunodiffusion analysis of E. coli strains carrying varying portions of the cap region, we identified a novel gene (dep) responsible for degradation of the capsular polymer of B. anthracis. The simultaneous presence of the cap region and the dep gene caused production of low‐molecular‐weight, degraded capsular polymer both in E. coli and in B. anthracis, whereas the cap region atone caused production of a high‐molecular‐weight capsule. The dep gene mapped immediately downstream of the cap region within a 1.8 kb fragment and was transcribed in the same direction. This fragment was sequenced and a 1401 bp open reading frame (ORF) was found that is predicted to encode a peptide with molecular weight of 51460. By in vitro transcription‐translation analysis, this ORF was shown to be the dep gene product. The deduced amino acid sequence of the dep product has sequence similarity to E. coli and mammalian γ‐glutamyltranspeptidase (GGT). However, the Dep protein did not have GGT activity. The Dep protein appears to be an enzyme that catalyses the hydrolysis of the poly‐D‐glutamic acid capsule. Although the biological functions of the dep gene are unknown, it is possible that low‐molecular‐weight, diffusible polyglutamates produced through the action of the dep gene may act to inhibit host defence mechanisms.
The ntrBC genes of Rhizobium leguminosarum are part of a complex operon subject to negative regulation
Authors: Patriarca E. J. , Riccio A. , Taté R. , Colonna‐Romano S. , Iaccarino M. , Defez R. 
Published: October 2006

SummaryWe report here that ntrB and ntrC genes of Rhizobium leguminosarum biovar phaseoli are cotranscribed with an open reading frame (called 0RF1) of unknown Unction. The promoter region of the 0RF1‐ntrB‐ntrC operon was mapped immediately upstream of ORF1 and two in vivo transcription initiation sites were identified, both preceded by −35/−10 promoter consensus sequences. Some major aspects differentiate ft leguminosarum from the enteric nitrogen regulatory system: the ntrBC genes are cotranscribed with 0RF1 which is homologous to an ORF located upstream of ntrBC of R. capsulatus and to the 0RF1 located upstream of the fis gene of Escherichia coir, ntrBC are not transcribed from a −24/−12 promoter and are only autogenously repressed. Moreover, the intracellular concentration of the NtrC protein increases when the bacterium is grown on ammonium salts, white under the same conditions the promoter of one of its target genes, glnII, is 12 times less active.
Chemotaxis plays a role in the social behaviour of Myxococcus xanthus
Authors: Shi Wenyuan , Köhler Thilo , Zusman David R. 
Published: October 2006

Summary Myxococcus xanthus is a Gram‐negative bacterium that glides on a solid surface and displays a wide range of social behaviour including microbial development. The frz genes are homologues to the chemotaxis genes of Escherichia coli and Salmonella typhimurium and have been shown to be involved in microbial development. However, chemotaxis has never been clearly demonstrated in Myxococcus. In this study, we showed that M. xanthus exhibited tactic movements to many chemicals when they were subjected to steep and stable chemical gradients. M. xanthus was observed to spread into areas with abundant nutrients like yeast extract or Casitone and avoid areas with no nutrients or repellents (short‐chain alcohols or DMSO. Responses to attractants and repellents were additive. Movement towards attractants or away from repellents required the frz genes and was correlated with methylation or demethylation of FrzCD, a methyl‐accepting taxis protein. Furthermore, the frz genes were found to be required for both fruiting body formation during starvation and swarming in nutrient‐rich medium. In wild‐type strains, cells near the colony edge were observed to swarm towards the surrounding growth medium and to contain highly methylated FrzCD; cells near the colony centre contained mainly demethylated FrzCD and showed directed movement towards the colony edge. FrzCD was also found to be methylated during the aggregation stage of fruiting body formation on agar but largely demethylated in cells shaken in liquid starvation media. An frzf mutant failed to exhibit directed cell movements and no longer showed modification of FrzCD under these conditions. These observations suggest that M. xanthus does show chemotactic movements, that these movements require the frz genes, and that chemotaxis plays a very important role in the social behaviour of this organism.
Evolution of penicillin resistance in Streptococcus pneumoniae; the role of Streptococcus mitis in the formation of a low affinity PBP2B in S. pneumoniae
Authors: Dowson Christopher G. , Coffey Tracey J. , Kell Christopher , Whiley Robert A. 
Published: October 2006

SummaryPenicillin‐resistant strains of Streptococcus pneumoniae possess forms of penicillin‐binding proteins (PBPs) that have a low affinity for penicillin compared to those from penicillin‐sensitive strains. PBP genes from penicillin‐resistant isolates are very variable and have a mosaic structure composed of blocks of nucleotides that are similar to those found in PBP genes from penicillin‐sensitive isolates and blocks that differ by up to 21%. These chromosomally encoded mosaic genes have presumably arisen following transformation and homologous recombination with PBP genes from a number of closely related species. This study shows that PBP2B genes from many penicillin‐resistant isolates of S. pneumoniae contain blocks of nucleotides originating from Streptococcus mitis. In several instances it would appear that this material alone is sufficient to produce a low affinity PBP2B. In other examples PBP2B genes possess blocks of nucleotides from S. mitis and at least one additional unidentified species. Mosaic structure was aiso found in the PBP2B genes of penicillin‐sensitive isolates of S. mitis or S. pneumoniae. These mosaics did not confer penicillin resistance but nevertheless reveal something of the extent to which localized recombination occurs in these naturally transformable streptococci.
The Hsp60 protein of Helicobacter pylori: structure and immune response in patients with gastroduodenal diseases
Authors: Macchia Giovanni , Massone Annalisa , Burroni Daniela , Covacci Antonello , Censini Stefano , Rappuoli Rino 
Published: October 2006

Summary Helicobacter pylori is a human pathogen that has been associated with gastritis, peptic ulcer and gastric carcinoma. The role of the direct action of H. pylori virulence factors and of the induction of autoreactive immunity in the development of chronic gastritis has not been clarified yet. Here we report the cloning and molecular characterization of a gene of H. pylori coding for a protein of 58kDa, recognized by sera of patients affected by H. pylori‐induced gastroduodenal diseases. This antigen is present in all the H. pylori strains tested and it belongs to the Hsp60 family of heat‐shock proteins, with high homology with other bacterial and eukaryotic proteins of the same family. This class of homologous proteins has been implicated in the induction of autoimmune disorders in different systems. The presence in infected patients of anti‐H. pylori Hsp60 antibodies, potentially cross‐reacting with the human homologue, and cross‐reactivity between human Hsp60 and a rabbit antiserum against H. pylori Hsp60 suggest that a role of this protein in gastroduodenal diseases is possible.
The filamentous haemagglutinin, a multifaceted adhesin produced by virulent Bordetella spp.
Authors: Locht Camille , Berlin Philippe , Menozzi Franco D. , Renauld† Genevieve 
Published: October 2006

SummaryFilamentous haemagglutinin (FHA) is the major attachment factor produced by virulent Bordetella spp. Similar to the other virulence factors, its production is tightly regulated by a two‐component system in response to environmental changes. Although of impressive size (c. 220 kDa), it is very efficiently released into the culture supernatant of Bordetella pertussis. Its biogenesis involves complex processing of a larger precursor with a calculated molecular mass of 370 kDa. Export of FHA into the culture medium depends on an outer membrane protein homologous to haemolysin accessory proteins. Purified extracellular FHA is able to increase the adherence of other pathogens to the host, which may contribute to super‐infection in whooping cough. Although FHA‐ mutants colonize lungs as efficiently as the wild‐type parent strains, immune responses against FHA appear to protect against colonization. Unlike many other adhesins, FHA expresses at least three different attachment activities, one specific for the CR3 integrins of macrophages, one involving a carbohydrate‐binding site, specific for interactions with cilia, and a heparin‐binding activity that may be important for interaction of B. pertussis with epithelial cells or extracellular matrices.
The partition (par) locus of pSC101 is an enhancer of plasmid incompatibility
Authors: Miller Christine A. , Cohen Stanley N. 
Published: October 2006

SummaryThe incompatibitity that pSC101‐derived plasmids express toward each other is mediated by directly repeated sequences (iterons) located near the plasmid's replication origin. We report here that the pSC101 par locus, which stabilizes plasmid inheritance in dividing cell populations and alters DNA superheliclty, can function as a cis‐acting enhancer of incompatibility, which we show is determined jointly by the copy number of the plasmid and the number of iterons per copy. A single synthetic 32 bp iteron sequence carried by the pUC19 plasmid confers strong pSC101‐specific incompatibility in the absence of any other pSC101 sites but requires the par locus to express strong incompatibility when carried by a lower‐copy‐number plasmid. We propose a model by which the par locus can enchance the apparently antagonistic processes of incompatibility and pSC101 DNA replication while concurrently facilitating plasmid distribution during cell division.
Expression of gene 19 of the conjugative plasmid R1 is controlled by RNase III
Authors: Koraimann Günther , Schroller Christa , Graus Hans , Angerer Doris , Teferle Karin , Högenauer Gregor 
Published: October 2006

SummarySpecific cleavage of mRNAs by RNase III has been shown to control the expression of several Escherichia coli genes. We show here that the expression of gene 19 of the conjugative resistance plasmid R1 is controlled in its expression by the same endoribonuclease. In vivo studies revealed that a DNA fragment of 150 nucleotides including a perfect 22 nucleotide inverted repeat in the gene 19 coding region is responsible for the low expression of the gene both at the protein and the RNA levels. By using a translational gene 19‐lacZ fusion in isogenic RNase III+ and RNase III‐ strains we could identify RNase III as the key element in the down‐regulation of gene 19 expression. The sequencing of in vitro generated and RNase Ill‐digested transcripts confirmed the in vivo studies and revealed the exact positions of the RNase III cleavage sites within the coding part of the gene 19 transcript. The in vitro determined RNase III cleavage of gene 19 mRNA was confirmed by in vivo primer extension analysis. Finally, we could show that an exchange of three nucleotides within the RNase III recognition site abolished RNase III cleavage in vitro.
The transcriptional activator HIyU of Vibrio cholerae: nucleotide sequence and role in virulence gene expression
Authors: Williams S. G. , Attridge S. R. , Manning P. A. 
Published: October 2006

SummaryHlyU upregulates expression of the haemolysin, HlyA, of Vibrio cholerae. DNA sequence analysis indicates that HlyU is an 11.9 kDa protein containing a putative helix‐turn‐helix motif and belonging to a family of small regulatory proteins, including NolR (Rhizobium meliloti), SmtB (Synechococcus PCC 7942) and ArsR (piasmids R773, Escherichia coli; p1258, Staphylococcus aureus; and pSX267, Staphylococcus xylosus). An hlyU mutant was constructed by insertional inactivation, and found to be deficient in the production of both the haemolysin and a 28kDa secreted protein. The mutant was assessed for virulence in the infant mouse cholera model, revealing a 100‐fold increase in the LD50.. This suggests that HlyU promotes expression of virulence determinant(s) in vivo.
An unusually small gene required for sporulation by Bacillus subtilis
Authors: Levin Petra Anne , Fan Nancy , Ricca Ezio , Driks Adam , Losick Richard , Cutting Simon 
Published: October 2006

SummaryWe report the cloning and characterization of an unusually small gene called spoVM whose product Is required for normal formation of the cortex and coat during sporulation in Bacillus subtilis. The spoVM gene is adjacent to, and in convergent orientation with, the B. subtilis homologue to the Escherichia coli gene for ribosomal protein L28. The spoVM open reading frame is only 26 codons in length and is capable of encoding a polypeptide of 3 kDa. The short length of spoVM was verified by means of complementation experiments with wild‐type and deletion‐mutated copies of the open reading frame and by engineering the synthesis of the spoVM gene product in E. coli. Transcription of spoVM was induced during the second hour of sporulation (approximately stage II) by the appearance of the sporulation RNA poly‐merase sigma factor, σ;E. Efficient transcription of spoVM additionally required the action of the sporulation DNA‐binding protein SpolllD. Because spoVM was not strongly required for the transcription of several genes expressed at late times in development, its protein product is likely to play a morphogenetic rather than a regulatory role in sporulation.
Intercellular signalling in Vibrio harveyi: sequence and function of genes regulating expression of luminescence
Authors: Bassler Bonnie L. , Wright Miriam , Showalter Richard E. , Silverman Michael R. 
Published: October 2006

SummaryDensity‐dependent expression of luminescence in Vibrio harveyi is regulated by the concentration of an extracellular signal molecule (autoinducer) in the culture medium. A recombinant clone that restored function to one class of spontaneous dim mutants was found to encode functions necessary for the synthesis of, and response to, a signal molecule. Sequence analysis of the region encoding these functions revealed three open reading frames, two (luxL and luxM) that are required for production of an autoinducer substance and a third (luxN) that is required for response to this signal substance. The LuxL and LuxM proteins are not similar in amino acid sequence to other proteins in the database, but the LuxN protein contains regions of sequence resembling both the histidine protein kinase and the response regulator domains of the family of two–component, signal transduction proteins. The phenotypes of mutants with luxL, luxM and luxN defects indicated that an additional signal–response system controlling density‐dependent expression of luminescence remains to be identified.
Suppression of a dominant G protein β‐subunit mutation in yeast by Gα protein expression
Authors: Zhang Meng , Tipper Donald J. 
Published: October 2006

Summary SCG1/GPA1, STE4, and STE18 encode the α, β and λ components of the G protein involved in mating pheromone signal transduction in Saccharomyces cerevisiae. Responses, including G1 arrest and expression of genes such as FUS1, are activated by βλ, which is negatively controlled by α(GDP), We previously demonstrated that overexpression of Scg1 suppresses responses to α factor and that expression of certain hybrids between Scg1 and mammalian Gα proteins has the same effect and also suppresses growth arrest in an scg1‐null mutant. Effects were attributed to sequestration of βλ. We now show that effects on growth rate, morphology and FUS1 expression are consistent with this model. The STE4HPL allele causes dominant activation of the response pathway, and is presumed to encode a β subunit insensitive to control by α(GDP). Scg1 overexpression suppresses the growth arrest due to STE4HPL; normal α‐factor responses and fertility are restored. A model based on sequestration of βγ reconciles this result with the apparent paradox that the same level of Scg1 overexpression inhibits responses and mating in wild‐type cells. A Gαi hybrid also restores growth and allows inefficient mating in the STEHPL strain.
Mechanism of expression of DNA repair gene vsr, an Escherichia coli gene that overlaps the DNA cytosine methylase gene, dcm
Authors: Dar Mubasher E. , Bhagwat Ashok S. 
Published: October 2006

SummaryThe DNA cytosine methylase gene of Escherichia coli, dem, overlaps an open reading frame (ORF) that continues in +1 register past the end of dcm. This ORF codes for a gene, vsr, that is required for a T:G to C:G base mismatch correction process. In this study, mutants that affect the level of expression of the two genes were constructed and characterized. Further, a previously isolated mutant, dcm‐6, was cloned and mutations within it were identified. Northern blots were used to identify dcm‐specific RNA species in wild type and dcm‐6 cells. Based on these studies we conclude that there is a six‐codon overlap between vsr and dcm. The two proteins appear to be made from a single RNA transcript and translation of dcm is required for the efficient synthesis of Vsr. Further, Vsr is active by itself and may not be produced as a fusion with Dem. This is the first example of chromosomal genes that overlap in their coding regions and produce proteins with distinct functions.
Isozymes of S‐adenosylmethionine synthetase are encoded by tandemly duplicated genes in Escherichia coli
Authors: Satishchandran C. , Taylor John C. , Markham George D. 
Published: October 2006

SummaryThe sole biosynthetic route to S‐adenosylmethionine, the primary biological alkylating agent, is catalysed by S‐adenosylmethionine synthetase (ATP: L‐methionine S‐adenosyltransferase). In Escherichia coli and Sal‐monella typhimunum numerous studies have located a structural gene (metK) for this enzyme at 63min on the chromosomal map. We have now identified a second structural gene for S‐adenosylmethionine synthetase in E. coli by DNA hybridization experiments with metK as the probe; we denote this gene as metX. The metX gene is located adjacent to metK with the gene order speA metK metX speC. The metK and metX genes are separated by ∼0.8kb. The metK and the metX genes are oriented convergently as indicated by DNA hybridization experiments using sequences from the 5′ and 3′ ends of metK. The metK gene product is detected immunochemically only in cells growing in minimal media, whereas the metX gene product is detected immunochemically in cells grown in rich media at all growth phases and in stationary phase in minimal media.Mutants in metK or metX were obtained by insertion of a kanamycin resistance element into the coding region of the cloned metK gene (metK:: kan), followed by use of homologous recombination to disrupt the chromosomal metK or metX gene. The metK::kan mutant thus prepared does not grow on minimal media but does grow normally on rich media, while the corresponding metX::kan mutant does not grow on rich media although it grows normally on minimal media. These results indicate that metK expression is essential for growth of E. coli on minimal media and metX expression is essential for growth on rich media. Our results demonstrate that Ado Met synthetase has an essential cellular and/or metabolic function. Furthermore, the growth phenotypes, as well as immunochemical studies, demonstrate that the two genes that encode S‐adenosylmethionine synthetase isozymes are differentially regulated. The mutations in metK and metX are highly unstable and readily yield kanamycin‐resistant cells in which the chromosomal location of the kanamycin‐resistance element has changed.
Characterization of pilQ, a new gene required for the biogenesis of type 4 fimbriae in Pseudomonas aeruginosa
Authors: Martin Paul R. , Hobbs Matthew , Free Patricia D. , Jeske Yvette , Mattick John S. 
Published: October 2006

SummaryType 4 fimbriae are produced by a variety of pathogens, in which they appear to function in adhesion to epithelial cells, and in a form of surface translocation called twitching motility. Using transposon mutagenesis of Pseudomonas aeruginosa, we have identified a new locus required for fimbrial assembly. This locus contains the gene pilQ which encodes a 77 kDa protein with an N‐terminal hydro‐phobic signal sequence characteristic of secretory proteins, pilQ mutants lack the spreading colony morphology characteristic of twitching motility, are devoid of fimbriae, and are resistant to the fimbrial‐specific bacteriophage PO4. The pilQ gene was mapped to Spel fragment 2, which is located at 0–5 minutes on the P. aeruginosa PAO1 chromosome, and thus it is not closely linked to the previously characterized pilA‐D, pilS,R or pilT genes. The pilQ region also contains ponA, aroK and aroB‐like genes in an organization very similar to that of corresponding genes in Escherichia coli and Haemophilus influenzae. The predicted amino acid sequence of PilQ shows homology to the PulD protein of Kleb‐siella oxytoca and related outer membrane proteins which have been found in association with diverse functions in other species including protein secretion, DNA uptake and assembly of filamentous phage. PilQ had the highest overall homology to an outer membrane antigen from Neisseria gonorrhoeae, encoded by omc, that may fulfil the same role in type 4 fimbrial assembly in this species.