bluuebunny/crossref_metadata_2025_split huggingface dataset:
Age‐related changes in cardiac autonomic control during sleep
Authors: Brandenberger Gabrielle , Viola Antoine U. , Ehrhart Jean , Charloux Anne , Geny Bernard , Piquard FranÇois , Simon Chantal 
Published: August 2003

SummaryAging is commonly associated with decreased sleep quality and increased periodic breathing (PB) that can influence heart rate variability (HRV). Cardiac autonomic control, as inferred from HRV analysis, was determined, taking into account the sleep quality and breathing patterns. Two groups of 12 young (21.1 ± 0.8 years) and 12 older (64.9 ± 1.9 years) volunteers underwent electroencephalographic, cardiac, and respiratory recordings during one experimental night. Time and frequency domain indices of HRV were calculated in 5‐min segments, together with electroencephalographic and respiratory power spectra. In the elderly, large R–R oscillations in the very‐low frequency (VLF) range emerged, that reflected the frequency of PB observed in 18% of the sleep time. PB occurred more frequently during rapid eye movement sleep (REM) sleep and caused a significant (P < 0.02) increase in the standard deviation of normal R–R intervals (SDNN) and absolute low‐frequency (LF) power. With normal respiratory patterns, SDNN, absolute VLF, LF, and high frequency (HF) power fell during each sleep stage (P < 0.01) compared with young subjects, with no significant sleep‐stage dependent variations. An overall decrease (P < 0.01) in normalized HF/(LF + HF) was observed in the elderly, suggesting a predominant loss of parasympathetic activity which may be related to decreased slow‐wave sleep duration. These results indicate that two distinct breathing features, implying different levels of autonomic drive to the heart, influence HRV in the elderly during sleep. The breathing pattern must be considered to correctly interpret HRV in the elderly.
Underlying sleep pathology may cause chronic high fatigue in shift‐workers
Authors: Hossain J. L. , Reinish L. W. , Kayumov L. , Bhuiya P. , Shapiro C. M. 
Published: August 2003

SummaryAbout 20–25% of the population in primary healthcare settings complains of chronic fatigue but this symptom has been under‐emphasized compared with sleepiness in clinical practice. Shift‐workers are particularly vulnerable because of various fatigue‐related personal and public morbidity and mortality. The goal of this cross‐sectional study was to explore if fatigue severity could be used as an independent predictive tool to identify underlying sleep pathology. The 21 most‐fatigued (study group) and 23 least‐fatigued (control) miners were selected on the basis of the Fatigue Severity Scale (FSS), which was administered to 195 subjects in an underground mine in Timmins, a town in northern Ontario. The two groups were matched for age, gender, and body mass index (BMI). Mean FSS score for the most‐fatigued subjects was 4.9 ± 0.5 and the least‐fatigued was 2.2 ± 0.5 (P < 0.0001). The subjects from each group were studied polysomnographically to identify sleep disorders. The polysomnographic data in 15 of 21 (71.4%) of the most‐fatigued subjects displayed significant sleep pathology compared with only three of 23 (13.0%) in the least‐fatigued subjects. Based on Fisher's exact test, the difference between the two groups was highly significant (P < 0.0001). Also, in the total subject pool (n = 195), the correlation between subjective fatigue and sleepiness was not very strong (Pearson's r = 0.45), suggesting that these two symptoms can be independent phenomena. It is concluded that chronic high fatigue can be an independent manifestation of underlying sleep pathology, which warrants independent subjective and objective assessment.
Investigating the interaction between the homeostatic and circadian processes of sleep–wake regulation for the prediction of waking neurobehavioural performance
Authors: Van Dongen Hans P. A. , Dinges David F. 
Published: August 2003

SummaryThe two‐process model of sleep regulation has been applied successfully to describe, predict, and understand sleep–wake regulation in a variety of experimental protocols such as sleep deprivation and forced desynchrony. A non‐linear interaction between the homeostatic and circadian processes was reported when the model was applied to describe alertness and performance data obtained during forced desynchrony. This non‐linear interaction could also be due to intrinsic non‐linearity in the metrics used to measure alertness and performance, however. Distinguishing these possibilities would be of theoretical interest, but could also have important implications for the design and interpretation of experiments placing sleep at different circadian phases or varying the duration of sleep and/or wakefulness. Although to date no resolution to this controversy has been found, here we show that the issue can be addressed with existing data sets. The interaction between the homeostatic and circadian processes of sleep–wake regulation was investigated using neurobehavioural performance data from a laboratory experiment involving total sleep deprivation. The results provided evidence of an actual non‐linear interaction between the homeostatic and circadian processes of sleep–wake regulation for the prediction of waking neurobehavioural performance.
Analysis of the biosynthetic gene cluster for the polyether antibiotic monensin in Streptomyces cinnamonensis and evidence for the role of monB and monC genes in oxidative cyclization
Authors: Oliynyk Markiyan , Stark Christian B. W. , Bhatt Apoorva , Jones Michelle A. , Hughes‐Thomas Zoë A. , Wilkinson Christopher , Oliynyk Zoryana , Demydchuk Yuliya , Staunton James , Leadlay Peter F. 
Published: August 2003

SummaryThe analysis of a candidate biosynthetic gene cluster (97 kbp) for the polyether ionophore monensin from Streptomyces cinnamonensis has revealed a modular polyketide synthase composed of eight separate multienzyme subunits housing a total of 12 extension modules, and flanked by numerous other genes for which a plausible function in monensin biosynthesis can be ascribed. Deletion of essentially all these clustered genes specifically abolished monensin production, while overexpression in S. cinnamonensis of the putative pathway‐specific regulatory gene monR led to a fivefold increase in monensin production. Experimental support is presented for a recently‐proposed mechanism, for oxidative cyclization of a linear polyketide intermediate, involving four enzymes, the products of monBI, monBII, monCI and monCII. In frame deletion of either of the individual genes monCII (encoding a putative cyclase) or monBII (encoding a putative novel isomerase) specifically abolished monensin production. Also, heterologous expression of monCI, encoding a flavin‐linked epoxidase, in S. coelicolor was shown to significantly increase the ability of S. coelicolor to epoxidize linalool, a model substrate for the presumed linear polyketide intermediate in monensin biosynthesis.
Nuclear magnetic resonance spectroscopy reveals the functional state of the signalling protein CheY in vivo in Escherichia coli
Authors: Hubbard Julia A. , MacLachlan Lesley K. , King Gavin W. , Jones Joanna J. , Fosberry Andrew P. 
Published: August 2003

SummaryTwo‐component signal transduction (TCST) pathways are regulatory systems that are highly homologous throughout the bacterial kingdom. Their established role in virulence and absence in vertebrates has made TCST an attractive target for therapeutic intervention. However, such systems have yet to yield success in the development of novel antibiotics. CheY serves as a prototype for the analysis of response regulator function. The protein structure exhibits several conformations by both X‐ray and nuclear magnetic resonance (NMR) analyses. Knowledge of which structures are relevant in vivo would be valuable in a rational drug design project. Our aim was to probe the in vivo conformation and ligand binding of CheY in Escherichia coli under resting conditions by in‐cell NMR methods. CheY was selectively labelled with 15N by the control of growth and expression conditions. NMR spectra obtained in vivo demonstrated that the Mg2+ complex was the predominant form even though cells were resuspended in metal‐free buffers and the intracellular free Mg2+ was low. In‐cell NMR also confirmed the uptake and in vivo binding mode to CheY of small‐molecular‐weight compounds identified in vitro. This paper reports the first observation of the structure and interactions with a potential drug of a regulator protein in its native host in vivo using NMR spectroscopy.
Specific targeting of a DNA‐binding protein to the SPP1 procapsid by interaction with the portal oligomer
Authors: Stiege Asita C. , Isidro Anabela , Dröge Anja , Tavares Paulo 
Published: August 2003

SummaryThe icosahedral procapsid of tailed bacteriophages is composed of a large number of identical subunits and of minor proteins found in a few copies. Proteins present in a very low copy number are targeted to the viral procapsid by an unknown mechanism. Bacteriophage SPP1 procapsids and mature virions contain two copies of gp7 on average. Gp7 forms stable complexes with the SPP1 portal protein gp6. Deletion of the gp6 carboxyl‐terminus and the mutation Y467→C localized in the same region prevent gp6–gp7 complex formation. Gp7 binds double‐stranded and single‐stranded DNA. Gp6 competes for this interaction, and purified gp6–gp7 complexes do not bind DNA. Procapsid structures assembled in the absence of gp6 or carrying the mutant gp6 Y467→C lack gp7. The gp6–gp7 interaction thus targets gp7 to the procapsid where the portal protein is localized asymmetrically at a single vertex of the icosahedral structure. The interaction between the two proteins is disrupted during viral assembly. Proteins homologous to gp6 and gp7 are coded by contiguous genes in a variety of phage genomes from Gram‐positive bacteria, suggesting that the gp6–gp7 complex is widespread in this group of phages. Transient association with the portal protein, an essential component of tailed bacteriophages and herpes viruses, provides a novel strategy to target minor proteins to the virion structure that might be operative in a large number of viruses.
Elongator's toxin‐target (TOT) function is nuclear localization sequence dependent and suppressed by post‐translational modification
Authors: Fichtner Lars , Jablonowski Daniel , Schierhorn Angelika , Kitamoto Hiroko K. , Stark Michael J. R. , Schaffrath Raffael 
Published: August 2003

SummaryThe toxin target (TOT) function of the Saccharomyces cerevisiae Elongator complex enables Kluyveromyces lactis zymocin to induce a G1 cell cycle arrest. Loss of a ubiquitin‐related system (URM1–UBA4 ) and KTI11 enhances post‐translational modification/proteolysis of Elongator subunit Tot1p (Elp1p) and abrogates its TOT function. Using TAP tagging, Kti11p contacts Elongator and translational proteins (Rps7Ap, Rps19Ap Eft2p, Yil103wp, Dph2p). Loss of YIL103w and DPH2 (involved in diphtheria toxicity) suppresses zymocicity implying that both toxins overlap in a manner mediated by Kti11p. Among the pool that co‐fractionates with RNA polymerase II (pol II) and nucleolin, Nop1p, unmodified Tot1p dominates. Thus, modification/proteolysis may affect association of Elongator with pol II or its localization. Consistently, an Elongator‐nuclear localization sequence (NLS) targets green fluorescent protein (GFP) to the nucleus, and its truncation yields TOT deficiency. Similarly, KAP120 deletion rescues cells from zymocin, suggesting that Elongator's TOT function requires NLS‐ and karyopherin‐dependent nuclear import.
GadE (YhiE) activates glutamate decarboxylase‐dependent acid resistance in Escherichia coli K‐12
Authors: Ma Zhuo , Gong Shimei , Richard Hope , Tucker Don L. , Conway Tyrrell , Foster John W. 
Published: August 2003

SummaryCommensal and pathogenic strains of Escherichia coli possess three inducible acid resistance systems that collaboratively protect cells against acid stress to pH 2 or below. The most effective system requires glutamate in the acid challenge media and relies on two glutamate decarboxylases (GadA and B) combined with a putative glutamate:γ‐aminobutyric acid antiporter (GadC). A complex network of regulators mediates induction of this system in response to various media, pH and growth phase signals. We report that the LuxR‐like regulator GadE (formerly YhiE) is required for expression of gadA and gadBC regardless of media or growth conditions. This protein binds directly to the 20 bp GAD box sequence found in the control regions of both loci. Two previously identified AraC‐like regulators, GadX and GadW, are only needed for gadA/BC expression under some circumstances. Overexpression of GadX or GadW will not overcome a need for GadE. However, overexpression of GadE can supplant a requirement for GadX and W. Data provided also indicate that GadX and GadE can simultaneously bind the area around the GAD box region and probably form a complex. The gadA, gadBC and gadE genes are all induced by low pH in exponential phase cells grown in minimal glucose media. The acid induction of gadA/BC results primarily from the acid induction of gadE. Constitutive expression of GadE removes most pH control over the glutamate decarboxylase and antiporter genes. The small amount of remaining pH control is governed by GadX and W. The finding that gadE mutations also diminish the effectiveness of the other two acid resistance systems suggests that GadE influences the expression of additional acid resistance components. The number of regulatory proteins (five), sigma factors (two) and regulatory feedback loops focused on gadA/BC expression make this one of the most intensively regulated systems in E. coli.
The type III secretion chaperone FlgN regulates flagellar assembly via a negative feedback loop containing its chaperone substrates FlgK and FlgL
Authors: Aldridge Phillip , Karlinsey Joyce , Hughes Kelly T. 
Published: August 2003

SummaryThe type III secretion (TTS) chaperones are small proteins that act either as cytoplasmic bodyguards, protecting their secretion substrates from degradation and aggregation, facilitators of their cognate substrate secretion or both. FlgN has been previously shown to be a TTS chaperone for the hook‐associated proteins FlgK and FlgL (FlgKL), and a translational regulator of the anti‐σ28 factor FlgM. Protein stability assays indicate that a flgN mutation leads to a dramatic decrease in the half‐life of intracellular FlgK. However, using gene reporter fusions to flgK we show that a flgN mutation does not affect the translation of a flgK–lacZ fusion. Quantification of FlgM protein levels showed that FlgKL inhibit the positive regulation on flgM translation by FlgN when secretion of FlgKL is inhibited. Suppressors of the motility‐defective phenotype of a flgN mutant were isolated and mapped to the clpXP and fliDST loci. Overexpression of flgKL on a plasmid also suppressed the motility defect of a flgN null mutant. These results suggest that FlgN is not required for secretion of FlgKL and that FlgN typifies a class of TTS chaperones that allows for the minimal amount of their substrates expression required in the assembly process by protecting the substrate from proteolysis. Our data leads us to propose a model in which the interaction between FlgN and FlgK or FlgL is a sensing mechanism to determine the stage of flagellar assembly. Furthermore, the interaction between FlgN and FlgK or FlgL inhibits the translational regulation of flgM via FlgN in response to the stage of flagellar assembly.
Regulation of tryptophan synthase gene expression in Chlamydia trachomatis
Authors: Wood Heidi , Fehlner‐Gardner Christine , Berry Jody , Fischer Elizabeth , Graham Bonnie , Hackstadt Ted , Roshick Christine , McClarty Grant 
Published: August 2003

SummaryWe previously reported that Chlamydia trachomatis expresses the genes encoding tryptophan synthase (trpA and trpB). The results presented here indicate that C. trachomatis also expresses the tryptophan repressor gene (trpR). The complement of genes regulated by tryptophan levels in C. trachomatis is limited to trpBA and trpR. trp gene expression was repressed if chlamydiae‐infected HeLa cells were cultured the presence of tryptophan and induced if grown in tryptophan‐depleted medium or in the presence of IFN‐γ. Furthermore, expression of the trp genes in strains which encode a functional tryptophan synthase is repressed when infected cells are cultured in the presence of the tryptophan precursor indole. Results from experiments with cycloheximide, an inhibitor of eukaryotic protein synthesis, indicate that in addition to the absolute size of the intracellular tryptophan pool, host competition for available tryptophan plays a key role in regulating expression of the trp genes. The tryptophan analogue, 5‐fluorotryptophan, repressed trp gene expression and induced the formation of aberrant organisms of C. trachomatis. The growth‐inhibitory properties of 5‐fluorotryptophan could be reversed with exogenous tryptophan but not indole. In total, our results indicate that the ability to regulate trp gene expression in response to tryptophan availability is advantageous for the intracellular survival of this organism. Furthermore, the fact that C. trachomatis has retained the capacity to respond to tryptophan limitation supports the view that the in vivo antichlamydial effect of IFN‐γ is via the induction of the tryptophan‐degrading enzyme, indoleamine 2,3‐dioxygenase.
Ena/VASP proteins contribute to Listeria monocytogenes pathogenesis by controlling temporal and spatial persistence of bacterial actin‐based motility
Authors: Auerbuch Victoria , Loureiro Joseph J. , Gertler Frank B. , Theriot Julie A. , Portnoy Daniel A. 
Published: August 2003

SummaryThe Listeria monocytogenes surface protein ActA mediates actin‐based motility by interacting with a number of host cytoskeletal components, including Ena/VASP family proteins, which in turn interact with actin and the actin‐binding protein profilin. We employed a bidirectional genetic approach to study Ena/VASP′s contribution to L. monocytogenes movement and pathogenesis. We generated an ActA allelic series within the defined Ena/VASP‐binding sites and introduced the resulting mutant L. monocytogenes into cell lines expressing different Ena/VASP derivatives. Our findings indicate that Ena/VASP proteins contribute to the persistence of both speed and directionality of L. monocytogenes movement. In the absence of the Ena/VASP proline‐rich central domain, speed consistency decreased by sixfold. In addition, the   Ena/VASP   F‐actin‐binding   region   increased directionality     of     bacterial     movement     by     fourfold. We further show that both regions of Ena/VASP enhanced L. monocytogenes cell‐to‐cell spread to a similar degree, although the Ena/VASP F‐actin‐binding region did so in an ActA‐independent manner. Surprisingly, our ActA allelic series enabled us to uncouple L. monocytogenes speed from directionality although both were controlled by Ena/VASP proteins. Lastly, we showed the pathogenic relevance of these findings by the observation that L. monocytogenes lacking   ActA   Ena/VASP‐binding   sites   were   up   to 400‐fold less virulent during an adaptive immune response.
A group II intron has invaded the genus Azotobacter and is inserted within the termination codon of the essential groEL gene
Authors: Ferat Jean‐Luc , Le Gouar Martine , Michel François 
Published: August 2003

SummaryA group II intron that was previously identified within Azotobacter  vinelandii by  polymerase  chain  reac‐tion with consensus primers has been completely sequenced, together with its flanking exons. In contrast to other bacterial members of group II, which are associated with mobile or other presumably non‐essential DNA, the A. vinelandii intron is inserted within the termination codon of the groEL coding sequence, which it changes from UAA to UAG. Both the host gene and the intron appear to be functional as (i) the ribozyme component of the intron self‐splices in vitro and (ii) both intron‐carrying and intronless versions of the single‐copy groEL gene from A. vinelandii complement groEL mutations in Escherichia coli. Moreover, analysis of nucleotide substitutions within and around a closely related intron sequence that is present at the same site in Azotobacter chroococcum provides indirect evidence of intron transposition posterior to the divergence of the two Azotobacter taxa. Somewhat surprisingly, however, analyses of RNA extracted from cells that had or had not undergone a heat shock show that the bulk of groEL transcripts end within the first 140 nucleotides of the intron. These findings are discussed in the light of our current knowledge of the biochemistry of group II introns.
A bacterial conjugation machinery recruited for pathogenesis
Authors: Seubert Anja , Hiestand Rosemarie , De La Cruz Fernando , Dehio Christoph 
Published: August 2003

SummaryType IV secretion systems (T4SS) are multicomponent transporters of Gram‐negative bacteria adapted to functions as diverse as DNA transfer in bacterial conjugation or the delivery of effector proteins into eukaryotic target cells in pathogenesis. The generally modest sequence conservation between T4SS may reflect their evolutionary distance and/or functional divergence. Here, we show that the establishment of intraerythrocytic parasitism by Bartonella tribocorum requires a putative T4SS, which shares an unprecedented level of sequence identity with the Trw conjugation machinery of the broad‐host‐range antibiotic resistance plasmid R388 (up to 80% amino acid identity for individual T4SS components). The highly conserved T4SS loci are collinear except for the presence of numerous tandem gene duplications in B. tribocorum, which mostly encode variant forms of presumed surface‐exposed pilus subunits. Conservation is not only structural, but also functional: R388 mutated in either trwD or trwH encoding essential T4SS components could be trans‐complemented for conjugation by the homologues of the B. tribocorum system. Conservation also includes the transcription regulatory circuit: both T4SS loci encode a highly homologous and interchangeable KorA/KorB repressor system that negatively regulates the expression of all T4SS components. This striking example of adaptive evolution reveals the capacity of T4SS to assume dedicated functions in either DNA transfer or pathogenesis over rather short evolutionary distance and implies a novel role for the conjugation systems of widespread broad‐host‐range plasmids in the evolution of bacterial pathogens.
Mycobacterial porins – new channel proteins in unique outer membranes
Authors: Niederweis Michael 
Published: August 2003

SummaryMycobacteria protect themselves with an outer lipid bilayer, which is the thickest biological membrane hitherto known and has an exceptionally low permeability rendering mycobacteria intrinsically resistant to many antibiotics. Pore proteins spanning the outer membrane mediate the diffusion of hydrophilic nutrients. Mycobacterium tuberculosis possesses at least two porins in addition to the low activity channel protein OmpATb. OmpATb is essential for adaptation of M. tuberculosis to low pH and survival in macrophages and mice. The channel activity of OmpATb is likely to play a major role in the defence of M. tuberculosis against acidification within the phagosome of macrophages. MspA is the main porin of Mycobacterium smegmatis. It forms a tetrameric complex with a single central pore of 10 nm length and a cone‐like structure. This structure differs clearly from that of the trimeric porins of Gram‐negative bacteria, which form one 4 nm long pore per monomer. The 45‐fold lower number of porins compared to Gram‐negative bacteria and the exceptional length of the pores are two major determinants of the low permeability of the outer membrane of M. smegmatis for hydrophilic solutes. The importance of the synergism between slow transport through the porins and drug efflux or inactivation for the development of drugs against M. tuberculosis is discussed.