bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Siderophore ofFrancisella tularensisand Role offslAin Siderophore Production
Authors: Sullivan Jonathan Tabb , Jeffery Erin Field , Shannon John D. , Ramakrishnan Girija
Published: May 2006

We determined that LVS and Schu S4 strains of the human pathogenFrancisella tularensisexpress a siderophore when grown under iron-limiting conditions. We purified this siderophore by conventional column chromatography and high-pressure liquid chromatography and used mass spectrometric analysis to demonstrate that it is structurally similar to the polycarboxylate siderophore rhizoferrin. The siderophore promoted the growth of LVS and Schu S4 strains in iron-limiting media. We identified a potential siderophore biosynthetic gene cluster encoded byfslABCDin theF. tularensisgenome. The first gene in the cluster,fslA, encodes a member of the superfamily of nonribosomal peptide synthetase-independent siderophore synthetases (NIS synthetases) characterized by the aerobactin synthetases IucA and IucC. We determined thatfslAis transcribed as part of an operon with downstream genefslBand that the expression of the locus is induced by iron starvation. A targeted in-frame nonpolar deletion offslAin LVS resulted in the loss of siderophore expression and in a reduced ability ofF. tularensisto grow under conditions of iron limitation. Siderophore activity and the ability to grow under iron limitation could be regained by introducing thefslA+gene on a complementing plasmid. Our results suggest that thefslA-dependent siderophore is important for survival ofF. tularensisin an iron-deficient environment.
Isolation and Characterization of VceC Gain-of-Function Mutants That Can Function with the AcrAB Multiple-Drug-Resistant Efflux Pump of
Escherichia coli
Authors: Vediyappan Govindsamy , Borisova Tatyana , Fralick Joe A.
Published: May 2006

VceC is the outer membrane component of the major facilitator (MF) VceAB-VceC multiple-drug-resistant (MDR) efflux pump of
Vibrio cholerae
. TolC is the outer membrane component of the resistance-nodulation-division AcrAB-TolC efflux pump of
Escherichia coli
. Although these proteins share little amino acid sequence identity, their crystal structures can be readily superimposed upon one another. In this study, we have asked if TolC and VceC are interchangeable for the functioning of the AcrAB and VceAB pumps. We have found that TolC can replace VceC to form a functional VceAB-TolC MDR pump, but VceC cannot replace TolC to form a functional AcrAB-VceC pump. However, we have been able to isolate gain-of-function (gof) VceC mutants which can functionally interface with AcrAB. These mutations map to four different amino acids located at the periplasmic tip of VceC. Chemical cross-linkage experiments indicate that both wild-type and gof mutant VceC can physically interact with the AcrAB complex, suggesting that these gof mutations are not affecting the recruitment of VceC to the AcrAB complex but rather its ability to functionally interface with the AcrAB pump.
Structural and Functional Characterization of Three Polyketide Synthase Gene Clusters in
Bacillus amyloliquefaciens
FZB 42
Authors: Chen Xiao-Hua , Vater Joachim , Piel Jörn , Franke Peter , Scholz Romy , Schneider Kathrin , Koumoutsi Alexandra , Hitzeroth Gabriele , Grammel Nicolas , Strittmatter Axel W. , Gottschalk Gerhard , Süssmuth Roderich D. , Borriss Rainer
Published: May 2006

Although bacterial polyketides are of considerable biomedical interest, the molecular biology of polyketide biosynthesis in
Bacillus
spp., one of the richest bacterial sources of bioactive natural products, remains largely unexplored. Here we assign for the first time complete polyketide synthase (PKS) gene clusters to
Bacillus
antibiotics. Three giant modular PKS systems of the
trans
-acyltransferase type were identified in
Bacillus amyloliquefaciens
FZB 42. One of them,
pks1
, is an ortholog of the
pksX
operon with a previously unknown function in the sequenced model strain
Bacillus subtilis
168, while the
pks2
and
pks3
clusters are novel gene clusters. Cassette mutagenesis combined with advanced mass spectrometric techniques such as matrix-assisted laser desorption ionization-time of flight mass spectrometry and liquid chromatography-electrospray ionization mass spectrometry revealed that the
pks1
(
bae
) and
pks3
(
dif
) gene clusters encode the biosynthesis of the polyene antibiotics bacillaene and difficidin or oxydifficidin, respectively. In addition,
B. subtilis
OKB105 (
pheA sfp
0
), a transformant of the
B. subtilis
168 derivative JH642, was shown to produce bacillaene, demonstrating that the
pksX
gene cluster directs the synthesis of that polyketide.
A New Integrative Conjugative Element Occurs in
Mycoplasma agalactiae
as Chromosomal and Free Circular Forms
Authors: Marenda Marc , Barbe Valérie , Gourgues Géraldine , Mangenot Sophie , Sagne Evelyne , Citti Christine
Published: May 2006

An integrative conjugative element, ICEA, was characterized in
Mycoplasma agalactiae
strain 5632, in which it occurs as multiple chromosomal copies and as a free circular form. The distribution of ICEA sequences in
M. agalactiae
strains and their occurrence in
Mycoplasma bovis
suggest the spreading of the element within or between species.
Mutationally Altered Signal Output in the Nart (NarX-Tar) Hybrid Chemoreceptor
Authors: Ward Scott M. , Bormans Arjan F. , Manson Michael D.
Published: May 2006

Signal-transducing proteins that span the cytoplasmic membrane transmit information about the environment to the interior of the cell. In bacteria, these signal transducers include sensor kinases, which typically control gene expression via response regulators, and methyl-accepting chemoreceptor proteins, which control flagellar rotation via the CheA kinase and CheY response regulator. We previously reported that a chimeric protein (Nart) that joins the ligand-binding, transmembrane, and linker regions of the NarX sensor kinase to the signaling and adaptation domains of the Tar chemoreceptor elicits a repellent response to nitrate and nitrite. As with NarX, nitrate evokes a stronger response than nitrite. Here we show that mutations targeting a highly conserved sequence (the P box) in the periplasmic domain alter chemoreception by Nart and signaling by NarX similarly. In particular, the G51R substitution converts Nart from a repellent receptor into an attractant receptor for nitrate. Our results underscore the conclusion that the fundamental mechanism of transmembrane signaling is conserved between homodimeric sensor kinases and chemoreceptors. They also highlight the plasticity of the coupling between ligand binding and signal output in these systems.
The
ectD
Gene, Which Is Involved in the Synthesis of the Compatible Solute Hydroxyectoine, Is Essential for Thermoprotection of the Halophilic Bacterium
Chromohalobacter salexigens
Authors: García-Estepa Raúl , Argandoña Montserrat , Reina-Bueno Mercedes , Capote Nieves , Iglesias-Guerra Fernando , Nieto Joaquín J. , Vargas Carmen
Published: May 2006

The halophilic bacterium
Chromohalobacter salexigens
synthesizes and accumulates compatible solutes in response to salt and temperature stress.
13
C-nuclear magnetic resonance analysis of cells grown in minimal medium at the limiting temperature of 45°C revealed the presence of hydroxyectoine, ectoine, glutamate, trehalose (not present in cells grown at 37°C), and the ectoine precursor,
N
γ-acetyldiaminobutyric acid. High-performance liquid chromatography analyses showed that the levels of ectoine and hydroxyectoine were maximal during the stationary phase of growth. Accumulation of hydroxyectoine was up-regulated by salinity and temperature, whereas accumulation of ectoine was up-regulated by salinity and down-regulated by temperature. The
ectD
gene, which is involved in the conversion of ectoine to hydroxyectoine, was isolated as part of a DNA region that also contains a gene whose product belongs to the AraC-XylS family of transcriptional activators. Orthologs of
ectD
were found within the sequenced genomes of members of the proteobacteria, firmicutes, and actinobacteria, and their products were grouped into the ectoine hydroxylase subfamily, which was shown to belong to the superfamily of Fe(II)- and 2-oxoglutarate-dependent oxygenases. Analysis of the ectoine and hydroxyectoine contents of an
ectABC ectD
mutant strain fed with 1 mM ectoine or hydroxyectoine demonstrated that
ectD
is required for the main ectoine hydroxylase activity in
C. salexigens
. Although in minimal medium at 37°C the wild-type strain grew with 0.5 to 3.0 M NaCl, with optimal growth at 1.5 M NaCl, at 45°C it could not cope with the lowest (0.75 M NaCl) or the highest (3.0 M NaCl) salinity, and it grew optimally at 2.5 M NaCl. The
ectD
mutation caused a growth defect at 45°C in minimal medium with 1.5 to 2.5 M NaCl, but it did not affect growth at 37°C at any salinity tested. With 2.5 M NaCl, the
ectD
mutant synthesized 38% (at 37°C) and 15% (at 45°C) of the hydroxyectoine produced by the wild-type strain. All of these data reveal that hydroxyectoine synthesis mediated by the
ectD
gene is thermoregulated and essential for thermoprotection of
C. salexigens
.
Different Roles of EIIAB
Man
and EII
Glc
in Regulation of Energy Metabolism, Biofilm Development, and Competence in
Streptococcus mutans
Authors: Abranches Jacqueline , Candella Melissa M. , Wen Zezhang T. , Baker Henry V. , Burne Robert A.
Published: May 2006

The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is the major carbohydrate transport system in oral streptococci. The mannose-PTS of
Streptococcus mutans
, which transports mannose and glucose, is involved in carbon catabolite repression (CCR) and regulates the expression of known virulence genes. In this study, we investigated the role of EII
Glc
and EIIAB
Man
in sugar metabolism, gene regulation, biofilm formation, and competence. The results demonstrate that the inactivation of
ptsG
, encoding a putative EII
Glc
, did not lead to major changes in sugar metabolism or affect the phenotypes of interest. However, the loss of EII
Glc
was shown to have a significant impact on the proteome and to affect the expression of a known virulence factor, fructan hydrolase (
fruA
). JAM1, a mutant strain lacking EIIAB
Man
, had an impaired capacity to form biofilms in the presence of glucose and displayed a decreased ability to be transformed with exogenous DNA. Also, the lactose- and cellobiose-PTSs were positively and negatively regulated by EIIAB
Man
, respectively. Microarrays were used to investigate the profound phenotypic changes displayed by JAM1, revealing that EIIAB
Man
of
S. mutans
has a key regulatory role in energy metabolism, possibly by sensing the energy levels of the cells or the carbohydrate availability and, in response, regulating the activity of transcription factors and carbohydrate transporters.
Utilization of the Methoxymalonyl-Acyl Carrier Protein Biosynthesis Locus for Cloning the Oxazolomycin Biosynthetic Gene Cluster from
Streptomyces albus
JA3453
Authors: Zhao Chunhua , Ju Jianhua , Christenson Steven D. , Smith Wyatt C. , Song Danfeng , Zhou Xiufen , Shen Ben , Deng Zixin
Published: May 2006

Oxazolomycin (OZM), a hybrid peptide-polyketide antibiotic, exhibits potent antitumor and antiviral activities. Using degenerate primers to clone genes encoding methoxymalonyl-acyl carrier protein (ACP) biosynthesis as probes, a 135-kb DNA region from
Streptomyces albus
JA3453 was cloned and found to cover the entire OZM biosynthetic gene cluster. The involvement of the cloned genes in OZM biosynthesis was confirmed by deletion of a 12-kb DNA fragment containing six genes for methoxymalonyl-ACP biosynthesis from the specific region of the chromosome, as well as deletion of the
ozmC
gene within this region, to generate OZM-nonproducing mutants.
Albomycin Uptake via a Ferric Hydroxamate Transport System ofStreptococcus pneumoniaeR6
Authors: Pramanik Avijit , Braun Volkmar
Published: May 2006

The antibiotic albomycin is highly effective againstStreptococcus pneumoniae, with an MIC of 10 ng/ml. The reason for the high efficacy was studied by measuring the uptake of albomycin intoS. pneumoniae. Albomycin was transported via the system that transports the ferric hydroxamates ferrichrome and ferrioxamine B. These two ferric hydroxamates antagonized the growth inhibition by albomycin and salmycin. Cross-inhibition of the structurally different ferric hydroxamates to both antibiotics can be explained by the similar iron coordination centers of the four compounds. [55Fe3+]ferrichrome and [55Fe3+]ferrioxamine B were taken up by the same transport system intoS. pneumoniae. Mutants in the adjacentfhuD,fhuB, andfhuGgenes were transport inactive and resistant to the antibiotics. Albomycin, ferrichrome, ferrioxamine B, and salmycin bound to the isolated FhuD protein and prevented degradation by proteinase K. Thefhulocus consisting of thefhuD,fhuB,fhuG, andfhuCgenes determines a predicted ABC transporter composed of the FhuD binding lipoprotein, the FhuB and FhuG transport proteins, and the FhuC ATPase. It is concluded that active transport of albomycin mediates the high antibiotic efficacy inS. pneumoniae.
The Superoxide Dismutases of
Bacillus anthracis
Do Not Cooperatively Protect against Endogenous Superoxide Stress
Authors: Passalacqua Karla D. , Bergman Nicholas H. , Herring-Palmer Amy , Hanna Philip
Published: May 2006

The
Bacillus anthracis
chromosome encodes four unique, putative superoxide dismutase (
sod
) genes. During exponential growth and sporulation,
sodA1
,
sodA2
, and
sodC
are transcribed constitutively throughout the growth cycle as individual genes. In contrast, the transcription of
sod15
occurs mainly during late exponential and sporulation phases as part of a four-gene operon that may be involved in spore formation. Vegetative cell and spore lysates of wild-type Sterne and superoxide dismutase deletion (
Δsod
) mutants show detectable SOD activity for SODA1 and SODA2, and protein analysis suggests that these two proteins form active homodimers and heterodimers. A comparison of the growth of parental versus Δ
sod
mutants under various chemical oxidative stresses indicates that Δ
sodA1
mutants are particularly sensitive to endogenously produced superoxide, whereas Δ
sodA2
, Δ
sod15
, and Δ
sodC
mutants remain as resistant to this stress as the parental strain. In addition, in mouse survival assays, Δ
sod15
and Δ
sodA1
were responsible for less end-point death, but the level of decreased virulence does not fall within a statistically significant range. Collectively, these data show that
sodA1
acts as a major protectant from intracellular superoxide stress, that
sod15
is transcribed as part of an operon that may play a role in cell morphology, and that
sodA2
and
sodC
may have minor roles that are not apparent in the conditions tested here.
Transcription of the
Bacillus subtilis gerK
Operon, Which Encodes a Spore Germinant Receptor, and Comparison with That of Operons Encoding Other Germinant Receptors
Authors: Igarashi Takao , Setlow Peter
Published: May 2006

The
gerA
,
gerB
, and
gerK
operons, which encode germinant receptors in spores of
Bacillus subtilis
, were transcribed only in sporulation, and their mRNA levels peaked initially ∼3 h before the initiation of accumulation of the spore's dipicolinic acid. After a rapid fall, levels of these mRNAs peaked again ∼5 h later. In one wild-type strain (PS832),
gerA
mRNA was the most abundant, with levels of
gerB
and
gerK
mRNAs ∼50% of that of
gerA
mRNA, whereas
gerB
mRNA was the most abundant in another wild-type strain (PY79). The synthesis of
gerK
mRNA in sporulation was abolished by loss of the forespore-specific RNA polymerase sigma factor, σ
G
, and induction of σ
G
synthesis in vegetative cells led to synthesis of
gerK
mRNA. SpoVT, a regulator of σ
G
-dependent gene expression, repressed
gerK
expression. The
gerK
promoter showed sequence similarities to σ
G
-dependent promoters, and deletion of elements of this putative promoter abolished
gerK
expression in sporulation.
Complete Cellulase System in the Marine BacteriumSaccharophagus degradansStrain 2-40T
Authors: Taylor Larry E. , Henrissat Bernard , Coutinho Pedro M. , Ekborg Nathan A. , Hutcheson Steven W. , Weiner Ronald M.
Published: May 2006

Saccharophagus degradansstrain 2-40 is a representative of an emerging group of marine complex polysaccharide (CP)-degrading bacteria. It is unique in its metabolic versatility, being able to degrade at least 10 distinct CPs from diverse algal, plant and invertebrate sources. TheS. degradansgenome has been sequenced to completion, and more than 180 open reading frames have been identified that encode carbohydrases. Over half of these are likely to act on plant cell wall polymers. In fact, there appears to be a full array of enzymes that degrade and metabolize plant cell walls. Genomic and proteomic analyses reveal 13 cellulose depolymerases complemented by seven accessory enzymes, including two cellodextrinases, three cellobiases, a cellodextrin phosphorylase, and a cellobiose phosphorylase. Most of these enzymes exhibit modular architecture, and some contain novel combinations of catalytic and/or substrate binding modules. This is exemplified by endoglucanase Cel5A, which has three internal family 6 carbohydrate binding modules (CBM6) and two catalytic modules from family five of glycosyl hydrolases (GH5) and by Cel6A, a nonreducing-end cellobiohydrolase from family GH6 with tandem CBM2s. This is the first report of a complete and functional cellulase system in a marine bacterium with a sequenced genome.
Ectopic Overexpression of Wild-Type and Mutant
hipA
Genes in
Escherichia coli
: Effects on Macromolecular Synthesis and Persister Formation
Authors: Korch Shaleen B. , Hill Thomas M.
Published: May 2006

Persistence is an epigenetic trait that allows a small fraction of bacteria, approximately one in a million, to survive prolonged exposure to antibiotics. In
Escherichia coli
an increased frequency of persisters, called “high persistence,” is conferred by mutations in the
hipA
gene, which encodes the toxin entity of the toxin-antitoxin module
hipBA
. The high-persistence allele
hipA7
was originally identified because of its ability to confer high persistence, but little is known about the physiological role of the wild-type
hipA
gene. We report here that the expression of wild-type
hipA
in excess of
hipB
inhibits protein, RNA, and DNA synthesis in vivo. However, unlike the RelE and MazF toxins, HipA had no effect on protein synthesis in an in vitro translation system. Moreover, the expression of wild-type
hipA
conferred a transient dormant state (persistence) to a sizable fraction of cells, whereas the rest of the cells remained in a prolonged dormant state that, under appropriate conditions, could be fully reversed by expression of the cognate antitoxin gene
hipB
. In contrast, expression of the mutant
hipA7
gene in excess of
hipB
did not markedly inhibit protein synthesis as did wild-type
hipA
and yet still conferred persistence to ca. 10% of cells. We propose that wild-type HipA, upon release from HipB, is able to inhibit macromolecular synthesis and induces a bacteriostatic state that can be reversed by expression of the
hipB
gene. However, the ability of the wild-type
hipA
gene to generate a high frequency of persisters, equal to that conferred by the
hipA7
allele, may be distinct from the ability to block macromolecular synthesis.
Molecular Basis of
l
-Rhamnose Branch Formation in Streptococcal Coaggregation Receptor Polysaccharides
Authors: Yoshida Yasuo , Ganguly Soumya , Bush C. Allen , Cisar John O.
Published: May 2006

The presence of
l
-rhamnose (Rha) branches in the coaggregation receptor polysaccharides (RPS) of
Streptococcus gordonii
38 and
Streptococcus oralis
J22 was eliminated by replacement of
wefB
with
ermAM
in these strains. The expression of this gene in
S. oralis
34 did not, however, result in the addition of Rha branches to the linear RPS of this strain, which is identical to that produced by the
wefB
-deficient mutant of
S. gordonii
38. This paradoxical finding was explained by a subtle difference in acceptor specificity of the galactose-1-phosphotransferases encoded by downstream
wefC
in
S. gordonii
38 and
wefH
in
S. oralis
34. These genes were distinguished by the unique ability of WefC to act on the branched acceptor formed by the action of WefB.
Evolution of Immunity and Host Chromosome Integration Site of P2-Like Coliphages
Authors: Karlsson Joakim L. , Cardoso-Palacios Carlos , Nilsson Anders S. , Haggård-Ljungquist Elisabeth
Published: May 2006

The amount and distribution of variation in the genomic region containing the genes in the lytic-lysogenic genetic switch and the sequence that determines the integration site into the host chromosome were analyzed for 38 P2-like phages from
Escherichia coli
. The genetic switch consists of two convergent mutually exclusive promoters, Pe and Pc, and two repressors, C and Cox. The immunity repressor C blocks the early Pe promoter, leading to the establishment of lysogeny. The Cox repressor blocks expression of Pc, allowing lytic growth. Phylogenetic analyses showed that the C and Cox proteins were distributed into seven distinct classes. The phylogenetic relationship differed between the two proteins, and we showed that homologous recombination plays a major role in creating alterations in the genetic switch, leading to new immunity classes. Analyses of the host integration site for these phages resulted in the discovery of a previously unknown site, and there were at least four regular integration sites. Interestingly, we found no case where phages of the same immunity class had different host attachment sites. The evolution of immunity and integration sites is complex, since it involves interactions both between the phages themselves and between phages and hosts, and often, both regulatory proteins and target DNA must change.
Rapid Succession within the
Veillonella
Population of a Developing Human Oral Biofilm In Situ
Authors: Palmer Robert J. , Diaz Patricia I. , Kolenbrander Paul E.
Published: May 2006

Streptococci are the primary component of the multispecies oral biofilm known as supragingival dental plaque; they grow by fermentation of sugars to organic acids, e.g., lactic acid. Veillonellae, a ubiquitous component of early plaque, are unable to use sugars; they ferment organic acids, such as lactate, to a mixture of shorter-chain-length acids, CO
2
, and hydrogen. Certain veillonellae bind to (coaggregate with) streptococci in vitro. We show that, between 4 and 8 hours into plaque development, the dominant strains of
Veillonella
change in their phenotypic characteristics (coaggregation and antibody reactivity) as well as in their genotypic characteristics (16S RNA gene sequences as well as strain level fingerprint patterns). This succession is coordinated with the development of mixed-species bacterial colonies. Changes in community structure can occur very rapidly in natural biofilm development, and we suggest that this process may influence evolution within this ecosystem.
The
Haemophilus influenzae
Type b
hcsA
and
hcsB
Gene Products Facilitate Transport of Capsular Polysaccharide across the Outer Membrane and Are Essential for Virulence
Authors: Sukupolvi-Petty Soila , Grass Susan , StGeme Joseph W.
Published: May 2006

Haemophilus influenzae
type b is a common cause of invasive bacterial disease, especially among children in underdeveloped countries. The type b polysaccharide capsule is a polymer of ribose and ribitol-5-phosphate and is a critical determinant of virulence. Expression of the type b capsule is dependent upon the
cap
b locus, which consists of three functionally distinct regions, designated regions 1 to 3. Region 3 contains the
hcsA
and
hcsB
genes, which share significant homology with genes that have been implicated in encapsulation in other pathogenic bacteria but have unclear functions. In this study, we inactivated
hcsA
alone,
hcsB
alone, and both
hcsA
and
hcsB
together and examined the effects of these mutations on polysaccharide transport and bacterial virulence properties. Inactivation of
hcsA
alone resulted in accumulation of polysaccharide in the periplasm and a partial decrease in surface-associated polysaccharide, whereas inactivation of
hcsB
alone or of both
hcsA
and
hcsB
together resulted in accumulation of polysaccharide in the periplasm and complete loss of surface-associated polysaccharide. All mutations eliminated serum resistance and abrogated bacteremia and mortality in neonatal rats. These results indicate that the
hcsA
and
hcsB
gene products have complementary functions involved in the transport of polysaccharide across the outer membrane and are essential for virulence.
Overexpression of PrfA Leads to Growth Inhibition ofListeria monocytogenesin Glucose-Containing Culture Media by Interfering with Glucose Uptake
Authors: Marr A. K. , Joseph B. , Mertins S. , Ecke R. , Müller-Altrock S. , Goebel W.
Published: May 2006

Listeria monocytogenesstrains expressing high levels of the virulence regulator PrfA (mutant PrfA* or wild-type PrfA) show strong growth inhibition in minimal media when they are supplemented with glucose but not when they are supplemented with glucose-6-phosphate compared to the growth of isogenic strains expressing low levels of PrfA. A significantly reduced rate of glucose uptake was observed in a PrfA*-overexpressing strain growing in LB supplemented with glucose. Comparative transcriptome analyses were performed with RNA isolated from aprfAmutant and an isogenic strain carrying multiple copies ofprfAorprfA* on a plasmid. These analyses revealed that in addition to high transcriptional up-regulation of the known PrfA-regulated virulence genes (group I), there was less pronounced up-regulation of the expression of several phage and metabolic genes (group II) and there was strong down-regulation of several genes involved mainly in carbon and nitrogen metabolism in the PrfA*-overexpressing strain (group III). Among the latter genes are thenrgAB,gltAB, andglnRAoperons (involved in nitrogen metabolism), theilvBoperon (involved in biosynthesis of the branched-chain amino acids), and genes for some ABC transporters. Most of the down-regulated genes have been shown previously to belong to a class of genes inBacillus subtiliswhose expression is negatively affected by impaired glucose uptake. Our results lead to the conclusion that excess PrfA (or PrfA*) interferes with a component(s) essential for phosphotransferase system-mediated glucose transport.
Transformation of 1,2-Dithiole-3-thiones Into 1,6,6aλ4-Trithiapentalenes via Reaction with Bromoethanones
Authors: Čmelík Richard , Pazdera Pavel
Published: May 2006

We report the reactions of derivatives of 5-amino-3-thioxo-3H-1,2-dithiole-4-carboxylic acid 1 with bromoethanones and acylation agents. Two different routes were used to obtain the products, 3-(acylmethylidene)-3H-1,2-dithioles 4. These compounds were synthesized by acylation of compounds 1 on the amino group, followed by the reaction with bromoethanones and excess of triethylamine. Another method was based on the inverted order of the mentioned reaction steps and in absence of a base. The treatment of 4 with thionyl chloride gave new unsaturated fused lactones 13 whereas thionation led to desired 1,6,6aλ4-trithiapentalenes 5. The structures of products and the reaction mechanisms are discussed.
Complexing capacity of soil fulvic acid for Cu2+, Cd2+, Mn2+, Ni2+, and Zn2+ measured by dialysis titration: a model based on soil fulvic acid aggregation
Authors: Rainville David P. , Weber James H.
Published: May 2006

The dialysis method of metal ion speciation is investigated as a technique to determine complexing capacities of soil fulvic acid (SFA) towards Cu2+, Cd2+, Mn2+, Ni2+, and Zn2+, between pH 5 and 7. The complexing capacity values for each metal ion usually increase as pH increases. At the same pH the values for Cd2+, Mn2+, Ni2+, and Zn2+, are similar, but Cu2+ values are significantly higher. The results are interpreted on the basis of a model involving the aggregation of SFA by metal ions, especially Cu2+.
Stereochemical studies. X. Synthesis of some epimeric δ-lactones
Authors: Cooke Ellen , Paradellis Themistocles C. , Edward John T.
Published: May 2006

Stereospecific syntheses are reported for the δ-lactones 3, 5, 8, 17, and 26.
Solvent extraction separation of Cr(VI)–Mo(VI)–W(VI), Zr(IV)–Hf(IV), and Se(IV)–Te(IV) with sulphoxides
Authors: Reddy Alavalapati Sambasiva , Reddy Bontha Ramachandra
Published: May 2006

Solvent extraction studies have been made on some metals in the same periodic group: Cr(VI)–Mo(VI)–W(VI), Zr(IV)–Hf(IV), and Se(IV)–Te(IV) from hydrochloric acid solutions by dialkyl and aryl sulphoxides. Separation of these metals from one another can be achieved by suitable choice of extraction conditions. The nature of extractable metal species has been elucidated.
Further justification for the exo-anomeric effect. Conformational analysis based on nuclear magnetic resonance spectroscopy of oligosaccharides
Authors: Thøgersen Henning , Lemieux Raymond U. , Bock Klaus , Meyer Bernd
Published: May 2006

Hard-sphere (HS) calculations predict three conformers for the branched B human blood group antigenic determinant (α LFuc(1 → 2)[α DGal(1 → 3)]βDGal) and two conformers for the linear tetrasaccharide (αLRha(1 → 2)αLRha(1 → 3)αLRha(1 → 3)βDGlcNAc), which constitutes a part of the repeating unit of the Shigellaflexneri O-antigen, which differ in conformational energy by less than 0.7 and 0.2 kcal/mol, respectively. However, a detailed 1H nmr study of specific interunit deshielding effects, quantitative treatment of spin-lattice relaxation times, and nuclear Overhauser enhancements requires that only one of the conformers thus predicted be, in fact, conformationally preferred in solution. These conformers are those predicted by hard-sphere exo-anomeric (HSEA) calculations.
Syntheses of derivatives of N-acetyl-D-lactosamine from D-lactal hexaacetate. Hexa-O-acetyl-2-deoxy-2-phthalimido-β-D-lactosyl chloride
Authors: Lemieux R. U. , Abbas S. Z. , Burzynska M. H. , Ratcliffe R. M.
Published: May 2006

Two reaction routes are presented for the preparation of hexa-O-acetyl-2-deoxy-2-phthalimido-β-D-lactosyl chloride (7) from lactal hexaacetate (1). One route involves, in the first stage, reaction of 1 with nitrosyl chloride and proceeds by way of benzyl 2-amino-2-deoxy-α-D-lactoside (4) as an intermediate. The other route, which is considered more efficient, involves reaction of 1 with cerie ammonium nitrate and sodium azide and involves the β-anomer (12) of 4 as an intermediate. The preparation of 7 is of interest as a reagent for the preparation of 2-amino-2-deoxy-β-D-lactosides. The procedures offer routes for the preparation of D-lactosamine.
Syntheses of core chain trisaccharides related to human blood group antigenic determinants
Authors: Lemieux R. U. , Abbas S. Z. , Chung B. Y.
Published: May 2006

Trisaccharides related to the core chain of human blood group determinants were synthesized by way of the phthalimido-chloride method; namely, β-D-Galp-(1 → 3)-β-D-GlcNAcp-(1 → 6)-D-Galp (3), β-D-Galp-(1 → 3)-β-D-GlcNAcp-(1 → 3)-D-Galp (5), β-D-Galp-(1 → 4)-β-D-GlcNAcp-(1 → 6)-D-Galp (4), and β-D-Galp-(1 → 4)-β-D-GlcNAcp-(1 → 3)-D-Galp (6). The syntheses of the 8-methoxy-carbonyloctyl β-glycosides of these trisaccharides are also reported.
Synthesis of βDGlcNAc(1 →6) and βDGal(1 → 4)βDGlcNAc(1 → 6) derivatives of the TN (αDGalNAc) human blood group determinant
Authors: Lemieux Raymond U. , Burzynska Maria Halina
Published: May 2006

In order to investigate the immunological properties of certain I blood group specific glycoproteins, the potential antigenic determinants βDGlcNAc(1 → 6)αDGalNAc and βDGal(1 → 4)βDGlcNAc(1 → 6)αDGalNAc attached as glycosides to 8-methoxy-carbonyloctanol were synthesized by way of the phthalimido-chloride method.
The synthesis and conformational properties of the diastereoisomeric βDGal(1→4)βDGlcNAc(1→6)6-C-CH3-D-Gal trisaccharides
Authors: Lemieux Raymond U. , Wong Ting C. , Thøgersen Henning
Published: May 2006

The trisaccharide βDGal(1 → 4)βDGlcNAc(1 → 6)DGal was known to be bound strongly by the so-called anti-I Ma monoclonal antibody. In order to help assess the conformation about the 1 → 6 glycosidic linkage that is accepted by the antibody combining site, the conformationally well-defined βDGal(1 → 4)βDGlcNAc(1 → 6) derivatives of 7-deoxy-L-glycero-D-galacto-heptopyranose and 7-deoxy-D-glycero-D-galacto-heptopyranose were synthesized. The conformational preferences for these trisaccharides were established by 1H nmr spectroscopy and rationalized by computer-assisted molecular modelling.
Thiol esters in organic synthesis. X. A new approach to 1,5-ketols and 5-hydroxy esters using S,S'-diethyl dithiomalonate as an ethanol carbanion equivalent
Authors: Liu Hsing-Jang , Oppong Isaac V.
Published: May 2006

Michael addition of S,S′-diethyl dithiomalonate to conjugated enones and α,β-unsaturated esters followed by reduction with Raney nickel gave rise to 1,5-ketols and 5-hydroxy esters respectively in good yields.
The crystal structure of 1-phenyl-3,5-dimethyl pyrazolium nitrate
Authors: Zukerman-Schpector J. , Castellano E. E. , Massabni A. C. , Pinto A. Derbli
Published: May 2006

The crystal structure of the title compound has been determined from diffractometric X-ray data and refined by full-matrix least-squares to a final R factor of 0.055 from 1099 independent reflections above background.The space group and cell dimensions are: P21/n, a = 7.916(2), b = 10.934(3), c = 13.638(1) Å, β = 97.37(1)°, with Z = 4.The 1-phenyl-3,5-dimethylpyrazole group was found to be positively charged, forming a strong ionic complex with the nitrate ion.The dihedral angle between the phenyl and pyrazole rings, corresponding to the minimum intramolecular van der Waals energy, was calculated and compared with those reported in different complexes of known structure, showing that there is a narrow range of rotational freedom about the N(1)—C(6) bond.
Modified phosphotriester method for chemical synthesis of ribooligonucleotides. Part I. Synthesis of riboundecaadenylate and two fragments constituting the sequence of R-17 translation control signal
Authors: Sung Wing L. , Narang Saran A.
Published: May 2006

A modified phosphotriester method has been successfully applied for the chemical synthesis of ribooligonucleotides. The starting material is a fully protected ribomononucleoside containing a 3′-phosphotriester group 5. The coupling reaction is performed using mesitylenesulfonyl tetrazole and purification of the product achieved using reversed phase column chromatography. The effectiveness of this method has been demonstrated by achieving an efficient and rapid synthesis of r-A7, r-A11, r5′-AAACAUGAGGA-3′, and r5′-UUACCCAUGU-3′ (R-17, translation control sequence).
Pyrones. VIII. Biosynthetic investigations of the fungal metabolite phacidin
Authors: Cyr Terry Donald , Poulton Gerald Arthur
Published: May 2006

Biosynthetic feeding experiments with singly and doubly 13C-labelled acetate show that phacidin (4-methoxy-6-nonanoyl-2H-pyran-2-one-3-carboxaldehyde) is formed from a heptaketide precursor. A similar feeding with sodium 13C-formate has shown that the methoxyl and aldehyde carbons are derived from the one-carbon pool.
Sulfur-free penicillin derivatives. VII. Multiple functionalization of 2-azetidinyl-3-methyl-2-butenoates
Authors: Wolfe Saul , Shaw Chia-Cheng
Published: May 2006

The title compounds, substituted with chlorine in the 4′-position and with phthalimido, 2,2,2-trichloroethoxycarbonylamino, or phenoxycarbonylamino in the 3′-position of the azetidinone ring, have been converted to bis-allylic formates via bromination of both methyl groups with excess N-bromosuccinimide, and displacement of both bromines by formate ions in methylene chloride solvent. The diformates react smoothly with a deficit of a boron halide to form E/Z mixtures of halogeno-formates, in which the E-isomer predominates. Depending on the 3′-azetidinyl substituent, these halogeno-formates undergo a second displacement with acetate either with retention of olefinic geometry or inversion of olefinic geometry. The mechanisms of these reactions are discussed, along with further transformations leading to hydroxylactones, halogenolactones, halogenohydrins, and other compounds. Examination of the proton magnetic resonance spectra of twenty-one compounds reveals that methylene protons cis to the β-lactam nitrogen atom of a methyl 2-azetidinyl-2-butenoate are found at higher field than methylene protons cis to the methoxycarbonyl group. This observation appears to provide a more reliable criterion for the assignment of configuration to geometrical isomers than one based on the magnitude of the chemical shift nonequivalence of the E and Z methylene protons.
Thermal explosions with variable thermal conductivity
Authors: Moise Avygdor , Pritchard Huw O.
Published: May 2006

Numerical solutions are presented for the case of a thermal explosion in a sphere, in which the thermal conductivity varies linearly with temperature. The behaviour of the critical temperature profiles and of the other critical parameters for variations in the thermal conductivity are demonstrated.
The infrared, Raman, and resonance Raman spectra and normal coordinate analysis of methyl and ethyl dithioacetate
Authors: Teixeira-Dias J. J. C. , Jardim-Barreto V. M. , Ozaki Y. , Storer A. C. , Carey P. R.
Published: May 2006

Infrared, Raman, and resonance Raman data are reported for ethyl and methyl dithioacetate together with data for their isotopically substituted analogs: CD3C(=S)SCH3, CH3C(=S)SCD3, 13CH3C(=S)SCH3, CH313C(=S)SCH3, CD3C(=S)SCH2CH3, CH3C(=S)SCD2CH3, and CH313C(=S)SCH2CH3. Based on these data and a normal coordinate analysis of methyl dithioacetate, assignments are proposed for the majority of bands appearing in the vibrational spectra. Using excitation wavelengths in the 324–356 nm region strong intensity enhancement is observed for Raman bands near 1195, 1100, 730, and 580 cm−1 which are assigned to stretching motions of the CCSSC skeleton. Raman excitation profiles are reported for the 1197 and 581 cm−1 bands of ethyl dithioacetate and the electronic absorbance peak near 305 nm is identified as the source of resonance Raman intensity enhancement.
The Raman and resonance Raman spectra of some substituted dialkyl dithioesters and their rotational isomers
Authors: Ozaki Y. , Storer A. C. , Carey P. R.
Published: May 2006

The Raman spectra of ethyl dithioacetate, methyl dithiopropionate, and ethyl thionoacetate are presented for the liquid phase at 25 °C and for the solid phase at approximately −130 °C. Certain spectral features disappear upon going from the liquid to the solid phase allowing the assignment of these bands to rotational isomers which are present in the liquid state only. The consequences of placing a tert-butyl group proximal to the CSS moiety in dithioesters are explored by considering the absorption, Raman, and resonance Raman spectra of ethyl dithiotrimethylacetate and tert-butyl dithioacetate. The resonance Raman spectra of the ionized and unionized forms of dithioacetic acid are also presented. The vibrational spectra of ethyl thiolacetate, and ethyl and methyl thionoacetate are compared to the spectra of the corresponding dithioesters.
A 13C nuclear magnetic resonance study of the reversible substituent migration in several 2-acyl and 2-silyl derivatives of tropolone. Troponoid-IV
Authors: Ménard D. , St-Jacques M. , Bagli J. F.
Published: May 2006

The energy barrier for the reversible substituent migration was determined for a number of 2-acyl and 2-silyl derivatives of tropolone. The energy barrier is found to be dependent on the nature of the migrating group. Asymmetric monosubstitution on the ring shifts the equilibrium in favor of one dynamic isomer. In the two cases studied (3-bromotropolone and 3-bromotropolone acetate) it is found that the equilibrium is shifted towards the isomer bearing the bromine atom at the 7-position.
The preparation of some thiochroman-3-ones and derivatives
Authors: Clark Peter D. , McKinnon David M.
Published: May 2006

The use of 2,3-dihydrobenzo[b]thiophene-2,3-dione as a source of 2-mercaptophenylacetic acid permits a convenient preparation of 2-carboxymethylthiophenylacetic acid or derivatives. These undergo a Dieckmann cyclization to 3-acetoxybenzothiopyrans, which may be hydrolysed to thiochroman-3-ones. The further reactions of some of these are described.
Modulation spectroscopy. Kinetics for the self-reactions of some α-aminoalkyl radicals in solution
Authors: Marriott Paul R. , Castelhano Arlindo L. , Griller David
Published: May 2006

The optical spectra and reaction kinetics of some a-aminoalkyl radicals, RĊHN(CH2R)2; R≡H, Me, Ph, were measured in solution using the technique of modulation spectroscopy. These radicals undergo diffusion controlled self-reaction with rate constants [Formula: see text]. When R≡Ph, the absorption spectrum has a well defined maximum at 346 nm; ε = 3390 M−1 cm−1, while the spectra when R≡H or Me were less intense [Formula: see text] and tailed into the visible. These spectra are substantially red-shifted when compared with those of simple alkyl radicals, an effect which is thought to be due to the interaction between the unpaired electron and the lone pair of electrons on nitrogen.
Synthèse et réactivité de quelques α-amino azocomposés: mécanisme de la cyclisation thermique en triazoles-1,2,4
Authors: Métra Pierre , Hamelin Jack
Published: May 2006

The reaction of O-mesitylenesulfonylhydroxylamine (MSH) with hydrazones leads to carbon amination with the formation of α-amino azo compounds. Thermolysis of these compounds affords 1,2,4-triazoles. Thsssse mechanism of this cyclization is discussed.
Dihydropyridines in synthesis and biosynthesis. III. Coupling of dihydropyridinetricarbonylchromium(0) complexes: bipyridyls
Authors: Kutney James P. , Kaczmarek Lucas , Mostowicz Danuta , Worth Brian R.
Published: May 2006

Reaction of 1,2- and 1,6-dihydro-3-ethyl-N-methyl pyridine tricarbonylchromium(0) complexes with methyllithium at low temperature afforded a high yield of dimeric tricarbonylchromium(0) complexes. Structures of the latter products were established by X-ray crystallographic analysis. Some chemistry of these novel compounds is described.
Stereoselective synthesis of (−)-α-multistriatin from D-glucose
Authors: Sum Phaik-Eng , Weiler Larry
Published: May 2006

D-Glucose was converted into (−)-α-multistriatin, the aggregation pheromone of the European elm bark beetle, via a highly stereoselective eighteen-step route.
Structure in the solid state and conformational analysis in solution of 1,4-diacetyl-1,4-dihydro-2,3-diphenylpyrazine, a potential antiaromatic heterocyclic compound
Authors: Armand Joseph , Bois Claudette , Philoche-Levisalles Michèle , Pouet Marie-José , Simonnin Marie-Paule
Published: May 2006

It is shown by X-ray crystallography that the 1,4-dihydropyrazine skeleton of 1,4-diacetyl-1,4-dihydro-2,3-diphenylpyrazine 2 has a boat shape. The C(2)–C(3) and C(5)–C(6) double bonds are localized; therefore 2 does not exist as an azahomoaromatic entity with 6 electrons delocalized on the ring and two electrons localized on one nitrogen atom. In the solid state 2 is in a Z, Z conformation. The 1H and 13C nmr spectra indicate that 2 exists as an equilibrium mixture of Z,E, E,E, and Z,Z conformers in CD2Cl2 at −80 °C. An unambiguous assignment of the different sets of signals has been obtained by nOe experiments performed at −80 °C. The conformer distribution is the following: 65% (Z,E), 22% (E,E), and 13% (Z,Z). The relatively low barrier to rotation about the carbonyl nitrogen bonds of the two amide groups [Formula: see text] is in line with a rather large C—N bond length (~1.375 Å) in the crystal.
The crystal and molecular structure of syn-2,11-diselena[3,3]metacyclophane and comparison with the dithia-analogue
Authors: Bushnell Gordon W. , Mitchell Reginald H.
Published: May 2006

The crystal structure of syn-2,11-diselena[3,3]metacyclophane, 1a, has been determined by single crystal X-ray diffraction and refined to an R-value of 0.039. The crystal structure is monoclinic with a = 1926(1), b = 801.4(3), c = 924(1) pm, β = 98.9(1)°, and is isomorphous with that of the analogous sulphur compound. The space group is P21/n with 4 molecules per cell, D(meas) = 1.733 g cm−3, D(calcd) = 1.726 g cm−3. The molecule has the syn-conformation with the largest possible Se—Se distance of 721.8 pm. The benzenoid rings form a dihedral angle of 19.1°. The distance between the internal aryl hydrogen atoms on rings 1 and 2 is 285.1 pm. The internal aryl C atoms are 314.6 pm apart. The 1Hmr solution spectra of 1a are consistent with the solid state structure, and can be explained without involving equilibration with an anti-conformer.
Biogenetic type solid phase phenol coupling synthesis of alkaloids. Prelycorane species
Authors: Apsimon J. W. , Dixit D. M.
Published: May 2006

The coupling of a norbelladine derivative supported on a modified styrene – 1% divinylbenzene copolymer proceeds in modest yield to provide a coupled product whose structure corresponds to the presently undescribed precursors to the Lycorane alkaloids. The orientation of phenol coupling (o–o-) is different to that observed (o–p-) on oxidation of the nonsupported substrates.
A highly stereoselective intramolecular aldol condensation. Part I. Nuclear magnetic resonance spectroscopic investigation of the stereochemistry of the products derived from the reaction of 2,2′-O-methylene-bis-D-glycerose with base
Authors: Szarek Walter A. , Pinto B. Mario , Haines Alan H. , Grindley T. Bruce
Published: May 2006

The intramolecular aldol condensation of 2,2′-O-methylene-bis-D-glycerose has been found to yield only two of the four possible diastereomeric products. At higher base concentration or prolonged reaction times, these products undergo a Cannizzaro reaction. The stereochemistry of the products derived from the aldol condensation has been established by means of labelling experiments and by examination of the products by 1Hmr and 13Cmr spectroscopy. The major and minor products of the reaction have been identified as being 2-C-hydroxymethyl-2,4-O-methylene-D,L-ribose (7) and 2-C-hydroxymethyl-2,4-O-methylene-D,L-xylose (8), respectively. The preferential stabilization of these products in the reaction by means of intramolecular hemiacetal formation is proposed as a driving force for the high degree of stereoselectivity; this possibility is supported by the isolation of the bicyclic systems expected from such a reaction. Conditions have been chosen such that 7 is formed exclusively.
Quadricyclane-norbornadiene isomerizations on alumina
Authors: Butler Douglas N. , Gupta Indranil
Published: May 2006

Standard synthetic steps have been used to convert 7-methylenequadricyclane into the spiro-cyclopropene 1 and the allene 2. These (and other) quadricyclanes are cleanly isomerized on alumina to the respective bicyclo[2.2.1]hepta-2,5-dienes 3 and 4.
The regioselectivity of the formation of dihydro- and tetrahydrocarbazoles by the Fischer indole synthesis
Authors: Reed G. W. Bryan , Cheng Peter T. W. , McLean Stewart
Published: May 2006

The cyclohexanone 3 and the cyclohexenone 13 have been prepared, converted to their phenylhydrazones, and subjected to the Fischer indole synthesis under conditions ranging from 7% to 60% sulfuric acid in methanol. The tetrahydrocarbazoles 4 and 5 were isolated in a 2:1 ratio in the sequence starting from 3 and no significant variation in the ratio was observed through the range of conditions used. In the sequence starting with 13, the dihydrocarbazoles 14 and 15 were isolated in a 1:1 ratio when 7% or 15% sulfuric acid was used; when more concentrated acid was used, normal Fischer products were not obtained but some transformation products were isolated from the complex mixture of products obtained. The observed regioselectivity of these reactions is not predicted from mechanistic considerations, and no mechanistic explanation for the results is apparent. As part of the proof of structure of 4 and 14, their N-benzyl derivatives were prepared from 1-benzyl-2-vinylindole by Diels–Alder reactions.