bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lon‐dependent proteolysis of CcdA is the key control for activation of CcdB in plasmid‐free segregant bacteria
Authors: Van Melderen Laurence , Bernard Philippe , Couturier Martine 
Published: October 2006

SummaryThe ccd locus contributes to the stability of plasmid F by post‐segregational killing of plasmid‐free bacteria. The ccdB gene product is a potent cell‐killing protein and its activity is negatively regulated by the CcdA protein, in this paper, we show that the CcdA protein is unstable and that the degradation of CcdA is dependent on the Lon protease. Differences in the stability of the killer CcdB protein and its antidote CcdA are the key to post‐segregational killing. Because the half‐life of active CcdA protein is shorter than that of active CcdB protein, persistence of the CcdB protein leads to the death of plasmid‐free bacterial segregants.
Mechanism of action of tetanus and botulinum neurotoxins
Authors: Montecucco Cesare , Schiavo Glampietro 
Published: October 2006

SummaryThe clostridial neurotoxins responsible for tetanus and botulism are metallo‐proteases that enter nerve cells and block neurotransmitter release via zinc‐dependent cleavage of protein components of the neuroexocytosis apparatus. Tetanus neurotoxin (TeNT) binds to the presynaptic membrane of the neuromuscular Junction and is internalized and transported retroaxonally to the spinal cord. Whilst TeNT causes spastic paralysis by acting on the spinal inhibitory interneurons, the seven serotypes of botullnum neurotoxins (BoNT) induce a flaccid paralysis because they intoxicate the neuromuscular junction. TeNT and BoNT serotypes B, D, F and G specifically cleave VAMP/synaptobrevin, a membrane protein of small synaptic vesicles, at different single peptide bonds. Proteins of the presynaptic membrane are specifically attacked by the other BoNTs: serotypes A and E cleave SNAP‐25 at two different sites located within the carboxyl terminus, whereas the specific target of serotype C is syntaxin.
When replication forks stop
Authors: Bierne Hélène , Michel Bénédicte 
Published: October 2006

SummaryDNA synthesis is an accurate and very processive phenomenon, yet chromosome replication does not proceed at a constant rate and progression of the replication fork can be impeded. Several structural and functional features of the template can modulate the rate of progress of the replication fork. These include DNA secondary structures, DNA damage and occupied protein‐binding sites. In addition, prokaryotes contain sites where replication is specifically arrested. DNA regions at which the replication machinery is blocked or transiently slowed could be particularly susceptible to genome rearrangements. Illegitimate recombination, a ubiquitous phenomenon which may have dramatic consequences, occurs by a variety of mechanisms. The observation that some rearrangements might be facilitated by a pause in replication could provide a clue in elucidating these processes. In support of this, some homologous and illegitimate recombination events have already been correlated with replication pauses or arrest sites.
A novel gene whose expression is regulated by the response‐regulator, SphR, in response to phosphate limitation in Synechococcus species PCC7942
Authors: Aiba Hirofumi , Mizuno Takeshi 
Published: October 2006

SummaryIn Synechococcus species PCC7942, the production of a subset of proteins is induced when it is grown in a phosphate‐limited medium. We previously suggested that a pair of cyanobacterial two‐component regulatory proteins, SphS (sensory‐kinase) and SphR (response‐regulator), may be involved in this particular response to phosphate limitation. Here it was found that a protein with an apparent molecular mass of 33 kDa became particularly abundant when the total cellular proteins from cells grown in a phosphate‐limited medium were analysed by SDS‐PAGE. A deletion mutant lacking both the sphS and the sphR genes failed to produce this 33 kDa protein in response to phosphate limitation. Thus it was reasonable to assume that this protein is a member of the group of proteins involved in the Synechococcus phosphate regulatory circuit (hence, it was named SphX). The SphX protein was purified to near homogeneity, and the corresponding structural gene was cloned. The determined nucleotide sequence revealed that the sphX gene encodes a novel protein with a calculated molecular mass of 36 374 Da, which was demonstrated to be located in the cytoplasmic membrane. Structural features of the SphX promoter were then clarified by determining its transcription start site, from which transcription was triggered in response to phosphate limitation. Furthermore, the putative response‐regulator, SphR, was demonstrated to bind to the upstream region of the SphX promoter by means of in vitro DNase I footprinting. From these results, we conclude that the sphX gene is a member of the Synechococcus phosphate regulatory circuit, in which the two signal‐transduction components, SphS and SphR, are crucially involved as transcriptional regulators. The SphX protein may play a role in phosphate assimilation in Synechococcus.
Characterization of broadly pleiotropic phenotypes caused by an hfq insertion mutation in Escherichia coli K‐12
Authors: Tsui Ho‐Ching Tiffany , Leung Hon‐Chiu Eastwood , Winkler Malcolm E. 
Published: October 2006

SummaryThe region immediately downstream from the miaA tRNA modification gene at 94.8 min contains the hfq gene and the hflA region, which are important in the bacteriophage Qβ and lambda life cycles. The roles of these genes in bacteria remain largely unknown. We report here the characterization of two chromosomal hfq insertion mutations. An omega (ω) cassette insertion near the end of hfq resulted in phenotypes only slightly different from the parent, although transcript mapping demonstrated that the insertion was completely polar on hfq expression. In contrast, an equally polar omega cassette insertion near the beginning of hfq caused pronounced pleiotropic phenotypes, including decreased growth rates and yields, decreased negative supercoiling of piasmids in stationary phase, increased cell size, osmosensitivity, increased oxidation of carbon sources, increased sensitivity to ultraviolet light, and suppression of bgl activation by hns mutations, hfq::ω mutant phenotypes were distinct from those caused by omega insertions early in the miaA tRNA modification gene. On the other hand, both hfq insertions interfered with lambda phage plaque formation, probably by means of polarity at the hflA region. Together, these results show that hfq function plays a fundamental role in Escherichia coli physiology and that hfq and the hflA region are in the amiB‐mutL‐miaA‐hfq‐hflX superoperon.
Bacteriophage‐like particle of Rochalimaea henselae
Authors: Anderson Burt , Goldsmith Cynthia , Johnson Angela , Padmalayam Indira , Baumstark Barbara 
Published: October 2006

SumnnaryAn extracellular particle approximately 40 nM in diameter was detected in culture supernatant from the fastidious bacterium Rochalimaea henselae. This particle has at least three associated proteins and contains 14kbp linear DNA segments that are heterogeneous in sequence. The 14kbp DNA was also present in R. henselae cells as an extrachromosomal element for all 14 strains tested. Despite attempts to induce lysis of R henselae, plaque formation was not observed. A similar particle, also containing 14 kbp DNA, was observed in Bartonella bacilliformis, and may be analogous to a bacteriophage that has been described elsewhere for B. bacilliformis.
A conserved DNA sequence is required for efficient gonococcal pilin antigenic variation
Authors: Wainwright Leslie Ann , Pritchard Kristen Hoikka , Selfert H. Steven 
Published: October 2006

SummaryAntigenic variation of the Neisseria gonorrhoeae pilus occurs when a variant pilin sequence from a silent locus recombines into the expression locus by predominantly unidirectional, homologous recombination. At the 3’end of all pilin loci lies a conserved ONA sequence, called the Sma/Cla repeat, which has sequence similarity to several recombinase‐binding sites, and therefore may be involved in pilin recombination. We have developed a novel reverse transcriptase/polymerase chain reaction (RT‐PCR) assay for direct monitoring of pilin recombination, and both RT‐PCR and phase variation were used to examine pilin recombination in a gonococcal strain that had had the pilE Sma/Cla repeat removed. Results from these experiments showed a decrease in pilin recombination when the Sma/Cla sequence was deleted from the expression locus, showing that a specialized site (Sma/Cla) is involved in efficient pilin recombination.
A non‐directed, hydroxylamine‐generated suppressor mutation in the P3 pairing region of the bacteriophage T4 td intron partially restores self‐splicing capability
Authors: Brown Michael D. , DeYoung Katherine L. , Hair Dwight H. 
Published: October 2006

SummaryHydroxylamine (HA) mutagenesis of an HA‐induced splicing‐defective bacteriophage T4 td intron mutant with a mutation in the intron P3 RNA pairing region was used to generate pseudorevertants. Because HA can only cause GC to AT transitions, the original mutant (H104A) could not undergo true reversion, yet the compensatory mutation on the opposite side of the P3 helix, which was complementary to the original H104A mutation, could occur. A pseudorevertant was isolated that contained both the original H104A mutation and the compensatory mutation HS9. By phenotypic and molecular genetic criteria, this double mutant (H104A‐HS9) was shown to be able to undergo significant RNA splicing, thus confirming the existence and functional importance of the long‐range P3 pairing region in this phage intron. The second‐site suppressor mutation (HS9) was isolated by phage cross and also exhibited some self‐splicing ability. A correlation exists between the strength of P3 helix Watson‐Crick base pairing and the apparent level of splicing when wild‐type, H104A, HS9, and H104A‐HS9 are compared. This suggests that the primary role of the P3 RNA pairing region in the T4 td intron is structural in contributing to the critical RNA secondary structure.
Structural and functional analysis of the promoter region involved in full expression of the cryIIIA toxin gene of Bacillus thuringiensis
Authors: Agaisse Hervé , Lereclus Didier 
Published: October 2006

SummaryThe promoter region of the cryIIIA toxin gene of Bacilius thuringiensis is composed of at least three domains: an upstream region extending from nucleotide positions ‐635 to ‐553 (with reference to the translational start codon of cryIIIA), an internal region extending from nucleotide positions ‐553 to ‐367, and a downstream region extending from nucleotide position 367 to +18. Deletion analysis and transcriptional fusions to the lacZ gene indicate that full expression of cryIIIA requires the association of the upstream and the downstream region. Primer extension experiments reveal a major cryIIIA transcript (designated T‐129) starting at nucleotide position ‐129 and another transcript (designated T‐558) starting at nucleotide position ‐558. Mutation in the ‐35 region of the promoter responsible for the initiation of T‐558 indicates that the upstream promoter is essential for full expression of cryIIIA, although not sufficient. Deletion of the DNA region carrying the previously described cryIIIA promoter does not affect full expression of cryIIIA and does not modify the 5 end of T‐129. Taken together, these results indicate that the 5 end of T‐129 is not a transcriptional start site. Therefore, we propose that T‐129 results from the processing of the mRNA initiated at the upstream promoter (T‐558), generating a stable mRNA with a 5’extremity at nucleotide position ‐129. From primer extension analysis and transcriptional fusions to lacZ, it appears that the upstream promoter is weakly but significantly expressed during the vegetative phase of growth, is activated at the onset of sporula‐tion and remains active at least until t5. However, unlike the promoters of other cry genes, this promoter is similar to σa‐dependent promoters rather than sporulation‐specific promoters. This promoter may therefore be transcribed by the EσA form of RNA polymerase. Activation at the onset of sporulation could result from the disappearance of a repressor, or the appearance of a stationary‐phase‐specific activator.
Cloning and sequencing of Vibrio cholerae mannose‐sensitive haemagglutinin pilin gene: localization of mshA within a cluster of type 4 pilin genes
Authors: Jonson Gunhild , Lebens Mikael , Holmgren Jan 
Published: October 2006

SummaryThe mannose‐sensitive haemagglutinin (MSHA) pilus that is associated with Vibrio cholerae strains of EI Tor biotype has been shown to be a potential colonization factor and protective antigen. The gene encoding the structural subunit of MSHA pili was cloned from size‐fractionated Sacl‐cleaved chromosomal DNA in the expression phage vector lambda ZAPII. Positive clones carried a c. 5.3 kb Sacl fragment and were identified on the basis of MSHA expression and hybridization with a synthetic oligonucleotide probe based upon the N‐terminus of MshA, the structural subunit of MSHA. The mshA gene vitas localized to a 2.6kb Sall‐EcoRI fragment, which was subcloned and shown to express MshA from Its own promoter in Escherichia coli. Nucleotide sequencing of the entire fragment revealed six open reading frames (ORFs) of which four were complete. The mshA gene encodes an 18094 Da prepilin protein, which in its mature form has a size of 17 436 Da. MshA is a type 4 (N‐MePhe) pilin protein that is more homologous to pilins produced by Pseudomonas aeruginosa and Neisseria gonorrhoeae than to TcpA, the structural subunit of the toxin‐coregulated pilus of V. cholerae. The protein seems to be directly involved in receptor binding, as an in‐frame mutation in the mshA gene was found to abolish both d‐mannose‐dependent haemagglutination and binding of V. cholerae bacteria to d‐mannose‐containing agarose beads. Three additional ORFs, all in the same transcriptional orientation as mshA, were found to encode type 4 pilin‐like proteins. A potential promoter with a sequence homologous to that of cAMP‐CRP‐activated promoters in E. coli was identified upstream of ORF3, the gene preceding mshA.
The HAP2,3,4 transcriptional activator is required for derepression of the yeast citrate synthase gene, CIT1
Authors: Rosenkrantz Mark , Keil Christine S. , Pennell Elizabeth A. , Devenish Louise J. 
Published: October 2006

SummaryThe yeast nuclear gene CIT1 encodes mitochondrial citrate synthase, which catalyses the first and rate‐limiting step of the tricarboxylic acid (TCA) cycle. Transcription of CIT1 is subject to glucose repression. Mutations in HAP2, HAP3 or HAP4 block derepression of a CIT1‐lacZ gene fusion. The HAP2,3,4 transcriptional activator also activates nuclear genes encoding components of the mitochondrial electron transport chain, and thus it co‐ordinates derepression of two major mitochondrial functions. Two DNA sequences resembling the consensus HAP2,3,4‐binding site (ACCAATNA) are located at approximately‐ 310 and ‐290, upstream of the CIT1 coding sequence. Deletion and mutation analysis indicates that the 290 element is critical for activation by HAP2,3,4. Glucose‐repressed expression of CIT1 is largely independent of HAP2,3,4, is repressed by glutamate, and requires a DNA sequence between ‐367 and ‐348. Evidence is presented for a second HAP2,3,4‐independent activation element located just upstream and overlapping the ‐290 HAP2,3,4 element.
Role of hns in the virulence phenotype of pathogenic salmonellae
Authors: Harrison Julia A. , Pickard Derek , Higgins Christopher F. , Khan Anjam , Chatfield Stephen N. , Ali Tahir , Dorman Charles J. , Hormaeche Carlos E. , Dougan Gordon 
Published: October 2006

SummaryA TnphoA‐generated mutant C5060, attenuated for virulence, was derived from the mouse‐virulent Salmonella typhimurium strain C5. This mutation, designated hns‐112::TnphoA, harbours the transposon in the 3 end of hns, with the alkaline phosphatase open reading frame in the opposite orientation to that of hns. Bacterial strains harbouring hns‐112::TnphoA were mucoid and had altered levels of DNA supercoiling, as monitored using pUC18 as a reporter plasmid. Transduction of hns‐112::TnphoA into mouse virulent strains, including S. typhimurium SL1344 and Salmonella enteritidis Se795, resulted in attenuation. When an independent hns mutation, harbouring a kanamycin‐resistance cassette inserted into the Kpnl site at base pair 237 of the hns gene, was introduced into S. typhimurium C5, the isolates were also attenuated. S. typhimurium C5 isolates harbouring the multicopy plasmid pGB651, which encodes the Escherichia coli hns gene, were partially attenuated in mice. Transductional analysis, using Tn10 insertions located close to the hns gene, showed that virulence could be restored In genetic crosses that eliminated the resident hns mutations. However, some hns+ transductants were stilt attenuated, suggesting that secondary attenuating lesions can accumulate in hns‐deficient strains. These studies show that the hns locus plays a role in Salmonella virulence.
The virulence regulator protein of Listeria ivanovii is highly homologous to PrfA from Listeria monocytogenes and both belong to the Crp‐Fnr family of transcription regulators
Authors: Lampidis Robert , Gross Roy , Sokolovic Zeljka , Goebel Werner , Kreft Jürgen 
Published: October 2006

SummaryThe two pathogenic Listeria species, L. ivanovii and L monocytogenes, can be differentiated biochemically and show different host ranges. Virulence of L. monocytogenes is dependent on the integrity of prfA which positively and coordinately regulates transcription of several virulence genes. Until now, a prfA homologue had not been identified in L. ivanovii. We have now cloned a chromosomal region from L. ivanovii comprising two genes with high homology to the picA and prfA genes from L. monocytogenes. Distal from prfA, an open reading frame highly homologous to a phosphorlbosyl pyrophosphate synthetase gene (prs) was newly identified, defining the border of the virulence gene cluster. Transcription of the gene for ivanolysin O and expression of other genes of the virulence gene cluster in L. ivanovii were dependent on PrfA. The pattern of PrfA‐dependent proteins (PdPs) expressed in L ivanovii was similar, but not identical to that of L. monocytogenes. The PrfA proteins, as predicted from nucleotide sequences of both pathogenic Listeria species, are very similar and show significant homology to the Crp‐Fnr family of global transcription regulators.
The human gastric pathogen Helicobacter pylori has a gene encoding an enzyme first classified as a mucinase in Vibrio cholerae
Authors: Smith Andrew W. , Chahal Bhajan , French Gary L. 
Published: October 2006

SummaryThe human bacterial pathogen Helicobacter pylori has been suggested to be the causative agent of the most common chronic infection of man. Since its first isolation in 1982, H. pylori has been associated with gastric and duodenal ulcer disease, and more recently, gastric cancer. The proteolytic digestion of gastric mucus by this microorganism has been suggested as an important mechanism by which its pathogenicity is at least partly exerted. Here we report the detection of protease activity in H. pylori total‐cell and supernatant extracts. On the basis that zinc metalloproteases are common microbial pathogenicity factors, we identified a single protein in H. pylori protein extracts with antibodies to the Pseudomonas aeruginosa elastase (a secreted zinc metallo‐protease). This same protein was identified by pooled serum from patients infected with H. pylori. We used the functional and immunological relationship between the P. aeruginosa elastase and the Vibrio cholerae haemagglutinin/protease (HAP) to clone the H. pylori hap gene, which was over 99% similar to the V. cholerae hap gene in the coding region. A 4 kb DNA fragment containing the entire cloned gene was highly unstable in Escherichia coli and Bacillus subtilis cloning vectors. We also demonstrated that a hap‐like gene sequence is present in ail nine Helicobacter species so far discovered. The V. cholerae HAP was first classified on the basis of its mucinase activity.
Nod factors of Rhizobium are a key to the legume door
Authors: Relić B. , Perret X. , Estrada‐García M. T. , Kopcinska J. , Golinowski W. , Krishnan H. B. , Pueppke S. G. , Broughton W. J. 
Published: October 2006

SummarySymbiotic interactions between rhizobia and legumes are largely controlled by reciprocal signal exchange. Legume roots excrete flavonoids which induce rhizobial nodulation genes to synthesize and excrete lopo‐oligosaccharide Nod factors. In turn, Nod factors provoke deformation of the root hairs and nodule primordium formation. Normally, rhizobia enter roots through infection threads in markedly curled root hairs. If Nod factors are responsible for symbiosis‐specific root hair deformation, they could also be the signal for entry of rhizobia into legume roots. We tested this hypothesis by adding, at inoculation, NodNGR‐factors to signal‐production‐deficient mutants of the broad‐host‐range Rhizobium sp. NGR234 and Bradyrhizobium japorticum strain USDA110. Between 10 −7 M and 10−6 M NodNGR factors permitted these NodABC mutants to penetrate, nodulate and fix nitrogen on Vigna unguiculata and Glycine max, respectively. NodNGR factors also allowed Rhizobium fredii strain USDA257 to enter and fix nitrogen on Calopogonium caeruleum, a non‐host. Detailed cytological investigations of V. unguiculata showed that the NodABC mutant UGR AnodABC, in the presence of NodNGR factors, entered roots in the same way as the wild‐type bacterium. Since infection threads were also present in the resulting nodules, we conclude that Nod factors are the signals that permit rhizobia to penetrate legume roots via infection threads.
Membrane association and role in DNA uptake of the Bacillus subtilis PriA anaiogue ComF1
Authors: Londoño‐Vallejo J. A. , Dubnau D. 
Published: October 2006

SummaryThe late competence protein ComF1 is required for genetic transformation in Bacillus subtilis. Because of the sequence similarities of ComF1 to known ATP‐dependent DNA helicases and translocases, we have hypothesized that this protein either unwinds bound double‐stranded DNA or helps in the translocation of the transforming single‐stranded DNA across the cell membrane. Two important implications of this hypothesis (the association of ComF1 with the membrane and its specific requirement for DNA uptake) have been tested in this report. Using cell fractionation techniques and Western blotting analysis, we show that ComF1 is located almost exclusively on the cell membrane and that it is membrane‐targeted independently of other competence proteins. Moreover, ComF1 behaves like an integral membrane protein in extractability and detergent partition assays. We also show that this protein is required for the DNA‐uptake step during transformation but not for DNA binding to the ceil surface. DNA uptake is blocked in strains with null mutations or in‐frame deletions in comF1 but also in strains that overproduce the ComF1 protein under competence conditions. This last observation suggests that ComF1 expression must be balanced with that of other competence proteins, with which it may interact to form a multisubunit complex for DNA uptake.